diff --git a/benches/transport_smtp.rs b/benches/transport_smtp.rs
index 13b8684..9288807 100644
--- a/benches/transport_smtp.rs
+++ b/benches/transport_smtp.rs
@@ -13,7 +13,7 @@ fn bench_simple_send(c: &mut Criterion) {
                 .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
                 .to("Hei <hei@domain.tld>".parse().unwrap())
                 .subject("Happy new year")
-                .body("Be happy!")
+                .body(String::from("Be happy!"))
                 .unwrap();
             let result = black_box(sender.send(&email));
             assert!(result.is_ok());
@@ -32,7 +32,7 @@ fn bench_reuse_send(c: &mut Criterion) {
                 .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
                 .to("Hei <hei@domain.tld>".parse().unwrap())
                 .subject("Happy new year")
-                .body("Be happy!")
+                .body(String::from("Be happy!"))
                 .unwrap();
             let result = black_box(sender.send(&email));
             assert!(result.is_ok());
diff --git a/examples/smtp.rs b/examples/smtp.rs
index e865e05..9314edb 100644
--- a/examples/smtp.rs
+++ b/examples/smtp.rs
@@ -8,7 +8,7 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
-        .body("Be happy!")
+        .body(String::from("Be happy!"))
         .unwrap();
 
     // Open a local connection on port 25
diff --git a/examples/smtp_selfsigned.rs b/examples/smtp_selfsigned.rs
index 8cf1927..378b032 100644
--- a/examples/smtp_selfsigned.rs
+++ b/examples/smtp_selfsigned.rs
@@ -14,7 +14,7 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
-        .body("Be happy!")
+        .body(String::from("Be happy!"))
         .unwrap();
 
     // Use a custom certificate stored on disk to securely verify the server's certificate
diff --git a/examples/smtp_starttls.rs b/examples/smtp_starttls.rs
index 7a1c7e0..5b83705 100644
--- a/examples/smtp_starttls.rs
+++ b/examples/smtp_starttls.rs
@@ -8,7 +8,7 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
-        .body("Be happy!")
+        .body(String::from("Be happy!"))
         .unwrap();
 
     let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
diff --git a/examples/smtp_tls.rs b/examples/smtp_tls.rs
index ca394f0..f77b5c2 100644
--- a/examples/smtp_tls.rs
+++ b/examples/smtp_tls.rs
@@ -8,7 +8,7 @@ fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new year")
-        .body("Be happy!")
+        .body(String::from("Be happy!"))
         .unwrap();
 
     let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
diff --git a/examples/tokio02_smtp_starttls.rs b/examples/tokio02_smtp_starttls.rs
index ca11f5a..37e2d3f 100644
--- a/examples/tokio02_smtp_starttls.rs
+++ b/examples/tokio02_smtp_starttls.rs
@@ -17,7 +17,7 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
-        .body("Be happy with async!")
+        .body(String::from("Be happy with async!"))
         .unwrap();
 
     let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
diff --git a/examples/tokio02_smtp_tls.rs b/examples/tokio02_smtp_tls.rs
index 412f361..6d40c80 100644
--- a/examples/tokio02_smtp_tls.rs
+++ b/examples/tokio02_smtp_tls.rs
@@ -17,7 +17,7 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
-        .body("Be happy with async!")
+        .body(String::from("Be happy with async!"))
         .unwrap();
 
     let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
diff --git a/examples/tokio03_smtp_starttls.rs b/examples/tokio03_smtp_starttls.rs
index 131e33b..4dc4e4b 100644
--- a/examples/tokio03_smtp_starttls.rs
+++ b/examples/tokio03_smtp_starttls.rs
@@ -17,7 +17,7 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
-        .body("Be happy with async!")
+        .body(String::from("Be happy with async!"))
         .unwrap();
 
     let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
diff --git a/examples/tokio03_smtp_tls.rs b/examples/tokio03_smtp_tls.rs
index 344460a..8d13071 100644
--- a/examples/tokio03_smtp_tls.rs
+++ b/examples/tokio03_smtp_tls.rs
@@ -17,7 +17,7 @@ async fn main() {
         .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
         .to("Hei <hei@domain.tld>".parse().unwrap())
         .subject("Happy new async year")
-        .body("Be happy with async!")
+        .body(String::from("Be happy with async!"))
         .unwrap();
 
     let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());
diff --git a/src/message/body.rs b/src/message/body.rs
index 9196184..1d620e7 100644
--- a/src/message/body.rs
+++ b/src/message/body.rs
@@ -1,95 +1,79 @@
-use std::borrow::Cow;
 use std::io::{self, Write};
+use std::ops::Deref;
 
 use crate::message::header::ContentTransferEncoding;
 
-/// A [`SinglePart`][super::SinglePart] body.
+/// A [`Message`][super::Message] or [`SinglePart`][super::SinglePart] body.
 #[derive(Debug, Clone)]
-pub struct Body(BodyInner);
+pub struct Body {
+    buf: Vec<u8>,
+    encoding: ContentTransferEncoding,
+}
 
+/// Either a `Vec<u8>` or a `String`.
+///
+/// If the content is valid utf-8 a `String` should be passed, as it
+/// makes for a more efficient `Content-Transfer-Encoding` to be choosen.
 #[derive(Debug, Clone)]
-enum BodyInner {
+pub enum MaybeString {
     Binary(Vec<u8>),
     String(String),
 }
 
 impl Body {
-    /// Returns the length of this `Body` in bytes.
+    /// Encode the supplied `buf`, making it ready to be sent as a body.
+    ///
+    /// Automatically chooses the most efficient encoding between
+    /// `7bit`, `quoted-printable` and `base64`.
+    pub fn new<B: Into<MaybeString>>(buf: B) -> Self {
+        let buf: MaybeString = buf.into();
+
+        let encoding = buf.encoding();
+        Self::new_impl(buf.into(), encoding)
+    }
+
+    /// Encode the supplied `buf`, using the provided `encoding`.
+    ///
+    /// Generally [`Body::new`] should be used.
+    ///
+    /// Returns an [`Err`] with the supplied `buf` untouched in case
+    /// the choosen encoding wouldn't have worked.
+    pub fn new_with_encoding<B: Into<MaybeString>>(
+        buf: B,
+        encoding: ContentTransferEncoding,
+    ) -> Result<Self, Vec<u8>> {
+        let buf: MaybeString = buf.into();
+
+        if !buf.is_encoding_ok(encoding) {
+            return Err(buf.into());
+        }
+
+        Ok(Self::new_impl(buf.into(), encoding))
+    }
+
+    /// Builds a new `Body` using a pre-encoded buffer.
+    ///
+    /// **Generally not you want.**
+    ///
+    /// `buf` shouldn't contain non-ascii characters, lines longer than 1000 characters or nul bytes.
     #[inline]
-    pub fn len(&self) -> usize {
-        match &self.0 {
-            BodyInner::Binary(b) => b.len(),
-            BodyInner::String(s) => s.len(),
-        }
+    pub fn dangerous_pre_encoded(buf: Vec<u8>, encoding: ContentTransferEncoding) -> Self {
+        Self { buf, encoding }
     }
 
-    /// Returns `true` if this `Body` has a length of zero, `false` otherwise.
-    #[inline]
-    pub fn is_empty(&self) -> bool {
-        match &self.0 {
-            BodyInner::Binary(b) => b.is_empty(),
-            BodyInner::String(s) => s.is_empty(),
-        }
-    }
-
-    /// Suggests the best `Content-Transfer-Encoding` to be used for this `Body`
-    ///
-    /// If the `Body` was created from a `String` composed only of US-ASCII
-    /// characters, with no lines longer than 1000 characters, then 7bit
-    /// encoding will be used, else quoted-printable will be choosen.
-    ///
-    /// If the `Body` was instead created from a `Vec<u8>`, base64 encoding is always
-    /// choosen.
-    ///
-    /// `8bit` and `binary` encodings are never returned, as they may not be
-    /// supported by all SMTP servers.
-    pub fn encoding(&self) -> ContentTransferEncoding {
-        match &self.0 {
-            BodyInner::String(s) if is_7bit_encoded(s.as_ref()) => {
-                ContentTransferEncoding::SevenBit
-            }
-            // TODO: consider when base64 would be a better option because of output size
-            BodyInner::String(_) => ContentTransferEncoding::QuotedPrintable,
-            BodyInner::Binary(_) => ContentTransferEncoding::Base64,
-        }
-    }
-
-    /// Encodes this `Body` using the choosen `encoding`.
-    ///
-    /// # Panic
-    ///
-    /// Panics if the choosen `Content-Transfer-Encoding` would end-up
-    /// creating an incorrectly encoded email.
-    ///
-    /// Could happen for example if `7bit` encoding is choosen when the
-    /// content isn't US-ASCII or contains lines longer than 1000 characters.
-    ///
-    /// Never panics when using an `encoding` returned by [`encoding`][Body::encoding].
-    pub fn encode(&self, encoding: ContentTransferEncoding) -> Cow<'_, Body> {
+    /// Encodes the supplied `buf` using the provided `encoding`
+    fn new_impl(buf: Vec<u8>, encoding: ContentTransferEncoding) -> Self {
         match encoding {
-            ContentTransferEncoding::SevenBit => {
-                assert!(
-                    is_7bit_encoded(self.as_ref()),
-                    "Body isn't valid 7bit content"
-                );
-
-                Cow::Borrowed(self)
-            }
-            ContentTransferEncoding::EightBit => {
-                assert!(
-                    is_8bit_encoded(self.as_ref()),
-                    "Body isn't valid 8bit content"
-                );
-
-                Cow::Borrowed(self)
-            }
-            ContentTransferEncoding::Binary => Cow::Borrowed(self),
+            ContentTransferEncoding::SevenBit
+            | ContentTransferEncoding::EightBit
+            | ContentTransferEncoding::Binary => Self { buf, encoding },
             ContentTransferEncoding::QuotedPrintable => {
-                let encoded = quoted_printable::encode_to_str(self);
-                Cow::Owned(Body(BodyInner::String(encoded)))
+                let encoded = quoted_printable::encode(buf);
+
+                Self::dangerous_pre_encoded(encoded, ContentTransferEncoding::QuotedPrintable)
             }
             ContentTransferEncoding::Base64 => {
-                let base64_len = self.len() * 4 / 3 + 4;
+                let base64_len = buf.len() * 4 / 3 + 4;
                 let base64_endings_len = base64_len + base64_len / LINE_MAX_LENGTH;
 
                 let mut out = Vec::with_capacity(base64_endings_len);
@@ -102,7 +86,7 @@ impl Body {
                     // modified Write::write_all to work around base64 crate bug
                     // TODO: remove once https://github.com/marshallpierce/rust-base64/issues/148 is fixed
                     {
-                        let mut buf: &[u8] = self.as_ref();
+                        let mut buf: &[u8] = buf.as_ref();
                         while !buf.is_empty() {
                             match writer.write(buf) {
                                 Ok(0) => {
@@ -118,32 +102,145 @@ impl Body {
                     }
                 }
 
-                Cow::Owned(Body(BodyInner::Binary(out)))
+                Self::dangerous_pre_encoded(out, ContentTransferEncoding::Base64)
+            }
+        }
+    }
+
+    /// Returns the length of this `Body` in bytes.
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.buf.len()
+    }
+
+    /// Returns `true` if this `Body` has a length of zero, `false` otherwise.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.buf.is_empty()
+    }
+
+    /// Returns the `Content-Transfer-Encoding` of this `Body`.
+    #[inline]
+    pub fn encoding(&self) -> ContentTransferEncoding {
+        self.encoding
+    }
+
+    /// Consumes `Body` and returns the inner `Vec<u8>`
+    #[inline]
+    pub fn into_vec(self) -> Vec<u8> {
+        self.buf
+    }
+}
+
+impl MaybeString {
+    /// Suggests the best `Content-Transfer-Encoding` to be used for this `MaybeString`
+    ///
+    /// If the `MaybeString` was created from a `String` composed only of US-ASCII
+    /// characters, with no lines longer than 1000 characters, then 7bit
+    /// encoding will be used, else quoted-printable will be choosen.
+    ///
+    /// If the `MaybeString` was instead created from a `Vec<u8>`, base64 encoding is always
+    /// choosen.
+    ///
+    /// `8bit` and `binary` encodings are never returned, as they may not be
+    /// supported by all SMTP servers.
+    pub fn encoding(&self) -> ContentTransferEncoding {
+        match &self {
+            Self::String(s) if is_7bit_encoded(s.as_ref()) => ContentTransferEncoding::SevenBit,
+            // TODO: consider when base64 would be a better option because of output size
+            Self::String(_) => ContentTransferEncoding::QuotedPrintable,
+            Self::Binary(_) => ContentTransferEncoding::Base64,
+        }
+    }
+
+    /// Returns whether the provided `encoding` would encode this `MaybeString` into
+    /// a valid email body.
+    fn is_encoding_ok(&self, encoding: ContentTransferEncoding) -> bool {
+        match encoding {
+            ContentTransferEncoding::SevenBit => is_7bit_encoded(&self),
+            ContentTransferEncoding::EightBit => is_8bit_encoded(&self),
+            ContentTransferEncoding::Binary => true,
+            ContentTransferEncoding::QuotedPrintable => {
+                // TODO: check
+
+                true
+            }
+            ContentTransferEncoding::Base64 => {
+                // TODO: check
+
+                true
             }
         }
     }
 }
 
-impl From<Vec<u8>> for Body {
-    #[inline]
-    fn from(b: Vec<u8>) -> Self {
-        Self(BodyInner::Binary(b))
+/// A trait for [`MessageBuilder::body`][super::MessageBuilder::body] and
+/// [`SinglePartBuilder::body`][super::SinglePartBuilder::body],
+/// which can either take something that can be encoded into [`Body`]
+/// or a pre-encoded [`Body`]
+pub trait IntoBody {
+    fn into_body(self, encoding: Option<ContentTransferEncoding>) -> Body;
+}
+
+impl<T> IntoBody for T
+where
+    T: Into<MaybeString>,
+{
+    fn into_body(self, encoding: Option<ContentTransferEncoding>) -> Body {
+        match encoding {
+            Some(encoding) => Body::new_with_encoding(self, encoding).expect("invalid encoding"),
+            None => Body::new(self),
+        }
     }
 }
 
-impl From<String> for Body {
-    #[inline]
-    fn from(s: String) -> Self {
-        Self(BodyInner::String(s))
+impl IntoBody for Body {
+    fn into_body(self, encoding: Option<ContentTransferEncoding>) -> Body {
+        let _ = encoding;
+
+        self
     }
 }
 
 impl AsRef<[u8]> for Body {
     #[inline]
     fn as_ref(&self) -> &[u8] {
-        match &self.0 {
-            BodyInner::Binary(b) => b.as_ref(),
-            BodyInner::String(s) => s.as_ref(),
+        self.buf.as_ref()
+    }
+}
+
+impl From<Vec<u8>> for MaybeString {
+    #[inline]
+    fn from(b: Vec<u8>) -> Self {
+        Self::Binary(b)
+    }
+}
+
+impl From<String> for MaybeString {
+    #[inline]
+    fn from(s: String) -> Self {
+        Self::String(s)
+    }
+}
+
+impl From<MaybeString> for Vec<u8> {
+    #[inline]
+    fn from(s: MaybeString) -> Self {
+        match s {
+            MaybeString::Binary(b) => b,
+            MaybeString::String(s) => s.into(),
+        }
+    }
+}
+
+impl Deref for MaybeString {
+    type Target = [u8];
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        match self {
+            Self::Binary(b) => b.as_ref(),
+            Self::String(s) => s.as_ref(),
         }
     }
 }
@@ -152,7 +249,7 @@ impl AsRef<[u8]> for Body {
 /// and no lines are longer than 1000 characters including the `\n` character.
 ///
 /// Most efficient content encoding available
-pub(crate) fn is_7bit_encoded(buf: &[u8]) -> bool {
+fn is_7bit_encoded(buf: &[u8]) -> bool {
     buf.is_ascii() && !contains_too_long_lines(buf)
 }
 
@@ -221,43 +318,31 @@ mod test {
 
     #[test]
     fn seven_bit_detect() {
-        let input = Body::from(String::from("Hello, world!"));
+        let encoded = Body::new(String::from("Hello, world!"));
 
-        let encoding = input.encoding();
-        assert_eq!(encoding, ContentTransferEncoding::SevenBit);
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::SevenBit);
+        assert_eq!(encoded.as_ref(), b"Hello, world!");
     }
 
     #[test]
     fn seven_bit_encode() {
-        let input = Body::from(String::from("Hello, world!"));
+        let encoded = Body::new_with_encoding(
+            String::from("Hello, world!"),
+            ContentTransferEncoding::SevenBit,
+        )
+        .unwrap();
 
-        let output = input.encode(ContentTransferEncoding::SevenBit);
-        assert_eq!(output.as_ref().as_ref(), b"Hello, world!");
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::SevenBit);
+        assert_eq!(encoded.as_ref(), b"Hello, world!");
     }
 
     #[test]
     fn seven_bit_too_long_detect() {
-        let input = Body::from("Hello, world!".repeat(100));
+        let encoded = Body::new("Hello, world!".repeat(100));
 
-        let encoding = input.encoding();
-        assert_eq!(encoding, ContentTransferEncoding::QuotedPrintable);
-    }
-
-    #[test]
-    #[should_panic]
-    fn seven_bit_too_long_fail() {
-        let input = Body::from("Hello, world!".repeat(100));
-
-        let _ = input.encode(ContentTransferEncoding::SevenBit);
-    }
-
-    #[test]
-    fn seven_bit_too_long_encode_quotedprintable() {
-        let input = Body::from("Hello, world!".repeat(100));
-
-        let output = input.encode(ContentTransferEncoding::QuotedPrintable);
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::QuotedPrintable);
         assert_eq!(
-            output.as_ref().as_ref(),
+            encoded.as_ref(),
             concat!(
                 "Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, wor=\r\n",
                 "ld!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, =\r\n",
@@ -283,63 +368,127 @@ mod test {
     }
 
     #[test]
-    #[should_panic]
-    fn seven_bit_invalid() {
-        let input = Body::from(String::from("Привет, мир!"));
+    fn seven_bit_too_long_fail() {
+        let result = Body::new_with_encoding(
+            "Hello, world!".repeat(100),
+            ContentTransferEncoding::SevenBit,
+        );
 
-        let _ = input.encode(ContentTransferEncoding::SevenBit);
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn seven_bit_too_long_encode_quotedprintable() {
+        let encoded = Body::new_with_encoding(
+            "Hello, world!".repeat(100),
+            ContentTransferEncoding::QuotedPrintable,
+        )
+        .unwrap();
+
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::QuotedPrintable);
+        assert_eq!(
+            encoded.as_ref(),
+            concat!(
+                "Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, wor=\r\n",
+                "ld!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, =\r\n",
+                "world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hell=\r\n",
+                "o, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!H=\r\n",
+                "ello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, worl=\r\n",
+                "d!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, w=\r\n",
+                "orld!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello=\r\n",
+                ", world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!He=\r\n",
+                "llo, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world=\r\n",
+                "!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, wo=\r\n",
+                "rld!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello,=\r\n",
+                " world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hel=\r\n",
+                "lo, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!=\r\n",
+                "Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, wor=\r\n",
+                "ld!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, =\r\n",
+                "world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!Hell=\r\n",
+                "o, world!Hello, world!Hello, world!Hello, world!Hello, world!Hello, world!H=\r\n",
+                "ello, world!Hello, world!"
+            )
+            .as_bytes()
+        );
+    }
+
+    #[test]
+    fn seven_bit_invalid() {
+        let result = Body::new_with_encoding(
+            String::from("Привет, мир!"),
+            ContentTransferEncoding::SevenBit,
+        );
+
+        assert!(result.is_err());
     }
 
     #[test]
     fn eight_bit_encode() {
-        let input = Body::from(String::from("Привет, мир!"));
+        let encoded = Body::new_with_encoding(
+            String::from("Привет, мир!"),
+            ContentTransferEncoding::EightBit,
+        )
+        .unwrap();
 
-        let out = input.encode(ContentTransferEncoding::EightBit);
-        assert_eq!(out.as_ref().as_ref(), "Привет, мир!".as_bytes());
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::EightBit);
+        assert_eq!(encoded.as_ref(), "Привет, мир!".as_bytes());
     }
 
     #[test]
-    #[should_panic]
     fn eight_bit_too_long_fail() {
-        let input = Body::from("Привет, мир!".repeat(200));
+        let result = Body::new_with_encoding(
+            "Привет, мир!".repeat(200),
+            ContentTransferEncoding::EightBit,
+        );
 
-        let _ = input.encode(ContentTransferEncoding::EightBit);
+        assert!(result.is_err());
     }
 
     #[test]
     fn quoted_printable_detect() {
-        let input = Body::from(String::from("Привет, мир!"));
+        let encoded = Body::new(String::from("Привет, мир!"));
 
-        let encoding = input.encoding();
-        assert_eq!(encoding, ContentTransferEncoding::QuotedPrintable);
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::QuotedPrintable);
+        assert_eq!(
+            encoded.as_ref(),
+            b"=D0=9F=D1=80=D0=B8=D0=B2=D0=B5=D1=82, =D0=BC=D0=B8=D1=80!".as_ref()
+        );
     }
 
     #[test]
     fn quoted_printable_encode_ascii() {
-        let input = Body::from(String::from("Hello, world!"));
+        let encoded = Body::new_with_encoding(
+            String::from("Hello, world!"),
+            ContentTransferEncoding::QuotedPrintable,
+        )
+        .unwrap();
 
-        let output = input.encode(ContentTransferEncoding::QuotedPrintable);
-        assert_eq!(output.as_ref().as_ref(), b"Hello, world!");
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::QuotedPrintable);
+        assert_eq!(encoded.as_ref(), b"Hello, world!");
     }
 
     #[test]
     fn quoted_printable_encode_utf8() {
-        let input = Body::from(String::from("Привет, мир!"));
+        let encoded = Body::new_with_encoding(
+            String::from("Привет, мир!"),
+            ContentTransferEncoding::QuotedPrintable,
+        )
+        .unwrap();
 
-        let output = input.encode(ContentTransferEncoding::QuotedPrintable);
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::QuotedPrintable);
         assert_eq!(
-            output.as_ref().as_ref(),
+            encoded.as_ref(),
             b"=D0=9F=D1=80=D0=B8=D0=B2=D0=B5=D1=82, =D0=BC=D0=B8=D1=80!".as_ref()
         );
     }
 
     #[test]
     fn quoted_printable_encode_line_wrap() {
-        let input = Body::from(String::from("Текст письма в уникоде"));
+        let encoded = Body::new(String::from("Текст письма в уникоде"));
 
-        let output = input.encode(ContentTransferEncoding::QuotedPrintable);
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::QuotedPrintable);
         assert_eq!(
-            output.as_ref().as_ref(),
+            encoded.as_ref(),
             concat!(
                 "=D0=A2=D0=B5=D0=BA=D1=81=D1=82 =D0=BF=D0=B8=D1=81=D1=8C=D0=BC=D0=B0 =D0=B2 =\r\n",
                 "=D1=83=D0=BD=D0=B8=D0=BA=D0=BE=D0=B4=D0=B5"
@@ -350,26 +499,34 @@ mod test {
 
     #[test]
     fn base64_detect() {
-        let input = Body::from(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
+        let input = Body::new(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
         let encoding = input.encoding();
         assert_eq!(encoding, ContentTransferEncoding::Base64);
     }
 
     #[test]
     fn base64_encode_bytes() {
-        let input = Body::from(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
+        let encoded = Body::new_with_encoding(
+            vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
+            ContentTransferEncoding::Base64,
+        )
+        .unwrap();
 
-        let output = input.encode(ContentTransferEncoding::Base64);
-        assert_eq!(output.as_ref().as_ref(), b"AAECAwQFBgcICQ==");
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::Base64);
+        assert_eq!(encoded.as_ref(), b"AAECAwQFBgcICQ==");
     }
 
     #[test]
     fn base64_encode_bytes_wrapping() {
-        let input = Body::from(vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9].repeat(20));
+        let encoded = Body::new_with_encoding(
+            vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9].repeat(20),
+            ContentTransferEncoding::Base64,
+        )
+        .unwrap();
 
-        let output = input.encode(ContentTransferEncoding::Base64);
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::Base64);
         assert_eq!(
-            output.as_ref().as_ref(),
+            encoded.as_ref(),
             concat!(
                 "AAECAwQFBgcICQABAgMEBQYHCAkAAQIDBAUGBwgJAAECAwQFBgcICQABAgMEBQYHCAkAAQIDBAUG\r\n",
                 "BwgJAAECAwQFBgcICQABAgMEBQYHCAkAAQIDBAUGBwgJAAECAwQFBgcICQABAgMEBQYHCAkAAQID\r\n",
@@ -382,19 +539,25 @@ mod test {
 
     #[test]
     fn base64_encode_ascii() {
-        let input = Body::from(String::from("Hello World!"));
+        let encoded = Body::new_with_encoding(
+            String::from("Hello World!"),
+            ContentTransferEncoding::Base64,
+        )
+        .unwrap();
 
-        let output = input.encode(ContentTransferEncoding::Base64);
-        assert_eq!(output.as_ref().as_ref(), b"SGVsbG8gV29ybGQh");
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::Base64);
+        assert_eq!(encoded.as_ref(), b"SGVsbG8gV29ybGQh");
     }
 
     #[test]
     fn base64_encode_ascii_wrapping() {
-        let input = Body::from("Hello World!".repeat(20));
+        let encoded =
+            Body::new_with_encoding("Hello World!".repeat(20), ContentTransferEncoding::Base64)
+                .unwrap();
 
-        let output = input.encode(ContentTransferEncoding::Base64);
+        assert_eq!(encoded.encoding(), ContentTransferEncoding::Base64);
         assert_eq!(
-            output.as_ref().as_ref(),
+            encoded.as_ref(),
             concat!(
                 "SGVsbG8gV29ybGQhSGVsbG8gV29ybGQhSGVsbG8gV29ybGQhSGVsbG8gV29ybGQhSGVsbG8gV29y\r\n",
                 "bGQhSGVsbG8gV29ybGQhSGVsbG8gV29ybGQhSGVsbG8gV29ybGQhSGVsbG8gV29ybGQhSGVsbG8g\r\n",
diff --git a/src/message/mimebody.rs b/src/message/mimebody.rs
index 814eae2..38d6ca2 100644
--- a/src/message/mimebody.rs
+++ b/src/message/mimebody.rs
@@ -1,6 +1,6 @@
 use crate::message::{
     header::{ContentTransferEncoding, ContentType, Header, Headers},
-    Body, EmailFormat,
+    EmailFormat, IntoBody,
 };
 use mime::Mime;
 use rand::Rng;
@@ -68,10 +68,15 @@ impl SinglePartBuilder {
     }
 
     /// Build singlepart using body
-    pub fn body<T: Into<Body>>(self, body: T) -> SinglePart {
+    pub fn body<T: IntoBody>(mut self, body: T) -> SinglePart {
+        let maybe_encoding = self.headers.get::<ContentTransferEncoding>().copied();
+        let body = body.into_body(maybe_encoding);
+
+        self.headers.set(body.encoding());
+
         SinglePart {
             headers: self.headers,
-            body: body.into(),
+            body: body.into_vec(),
         }
     }
 }
@@ -101,7 +106,7 @@ impl Default for SinglePartBuilder {
 #[derive(Debug, Clone)]
 pub struct SinglePart {
     headers: Headers,
-    body: Body,
+    body: Vec<u8>,
 }
 
 impl SinglePart {
@@ -111,57 +116,26 @@ impl SinglePart {
         SinglePartBuilder::new()
     }
 
-    /// Creates a singlepart builder using 7bit encoding
-    ///
-    /// 7bit encoding is the most efficient encoding available,
-    /// but it requires the body only to consist of US-ASCII characters,
-    /// with no lines longer than 1000 characters.
-    ///
-    /// When in doubt use [`SinglePart::builder`] instead, which
-    /// chooses the best encoding based on the body.
-    ///
-    /// # Panics
-    ///
-    /// The above conditions are checked when the Body gets encoded
-    #[inline]
+    #[doc(hidden)]
+    #[deprecated = "Replaced by SinglePart::builder(), which chooses the best Content-Transfer-Encoding based on the provided body"]
     pub fn seven_bit() -> SinglePartBuilder {
         Self::builder().header(ContentTransferEncoding::SevenBit)
     }
 
-    /// Creates a singlepart builder using quoted-printable encoding
-    ///
-    /// quoted-printable encoding should be used when the body may contain
-    /// lines longer than 1000 characters or a few non US-ASCII characters may be present.
-    /// If the body contains many non US-ASCII characters, [`SinglePart::base64`]
-    /// should be used instead, since it creates a smaller output compared
-    /// to quoted-printable.
-    ///
-    /// When in doubt use [`SinglePart::builder`] instead, which
-    /// chooses the best encoding based on the body.
-    #[inline]
+    #[doc(hidden)]
+    #[deprecated = "Replaced by SinglePart::builder(), which chooses the best Content-Transfer-Encoding based on the provided body"]
     pub fn quoted_printable() -> SinglePartBuilder {
         Self::builder().header(ContentTransferEncoding::QuotedPrintable)
     }
 
-    /// Creates a singlepart builder using base64 encoding
-    ///
-    /// base64 encoding must be used when the body is composed of mainly
-    /// non-text data.
-    ///
-    /// When in doubt use [`SinglePart::builder`] instead, which
-    /// chooses the best encoding based on the body.
-    #[inline]
+    #[doc(hidden)]
+    #[deprecated = "Replaced by SinglePart::builder(), which chooses the best Content-Transfer-Encoding based on the provided body"]
     pub fn base64() -> SinglePartBuilder {
         Self::builder().header(ContentTransferEncoding::Base64)
     }
 
-    /// Creates a singlepart builder using 8bit encoding
-    ///
-    /// Some SMTP servers might not support 8bit bodies.
-    ///
-    /// When in doubt use [`SinglePart::builder`] instead, which
-    /// chooses the best encoding based on the body.
-    #[inline]
+    #[doc(hidden)]
+    #[deprecated = "Replaced by SinglePart::builder(), which chooses the best Content-Transfer-Encoding based on the provided body"]
     pub fn eight_bit() -> SinglePartBuilder {
         Self::builder().header(ContentTransferEncoding::EightBit)
     }
@@ -174,7 +148,7 @@ impl SinglePart {
 
     /// Read the body from singlepart
     #[inline]
-    pub fn body(&self) -> &Body {
+    pub fn raw_body(&self) -> &[u8] {
         &self.body
     }
 
@@ -190,15 +164,7 @@ impl EmailFormat for SinglePart {
     fn format(&self, out: &mut Vec<u8>) {
         out.extend_from_slice(self.headers.to_string().as_bytes());
         out.extend_from_slice(b"\r\n");
-
-        let encoding = self
-            .headers
-            .get::<ContentTransferEncoding>()
-            .copied()
-            .unwrap_or_else(|| self.body.encoding());
-        let encoded = self.body.encode(encoding);
-
-        out.extend_from_slice(encoded.as_ref().as_ref());
+        out.extend_from_slice(&self.body);
         out.extend_from_slice(b"\r\n");
     }
 }
@@ -629,11 +595,13 @@ mod test {
                            "\r\n",
                            "--F2mTKN843loAAAAA8porEdAjCKhArPxGeahYoZYSftse1GT/84tup+O0bs8eueVuAlMK\r\n",
                            "Content-Type: application/pgp-encrypted\r\n",
+                           "Content-Transfer-Encoding: 7bit\r\n",
                            "\r\n",
                            "Version: 1\r\n",
                            "--F2mTKN843loAAAAA8porEdAjCKhArPxGeahYoZYSftse1GT/84tup+O0bs8eueVuAlMK\r\n",
                            "Content-Type: application/octet-stream; name=\"encrypted.asc\"\r\n",
                            "Content-Disposition: inline; filename=\"encrypted.asc\"\r\n",
+                           "Content-Transfer-Encoding: 7bit\r\n",
                            "\r\n",
                            "-----BEGIN PGP MESSAGE-----\r\n",
                            "wV4D0dz5vDXklO8SAQdA5lGX1UU/eVQqDxNYdHa7tukoingHzqUB6wQssbMfHl8w\r\n",
@@ -688,11 +656,13 @@ mod test {
                            "\r\n",
                            "--F2mTKN843loAAAAA8porEdAjCKhArPxGeahYoZYSftse1GT/84tup+O0bs8eueVuAlMK\r\n",
                            "Content-Type: text/plain\r\n",
+                           "Content-Transfer-Encoding: 7bit\r\n",
                            "\r\n",
                            "Test email for signature\r\n",
                            "--F2mTKN843loAAAAA8porEdAjCKhArPxGeahYoZYSftse1GT/84tup+O0bs8eueVuAlMK\r\n",
                            "Content-Type: application/pgp-signature; name=\"signature.asc\"\r\n",
                            "Content-Disposition: attachment; filename=\"signature.asc\"\r\n",
+                           "Content-Transfer-Encoding: 7bit\r\n",
                            "\r\n",
                            "-----BEGIN PGP SIGNATURE-----\r\n",
                             "\r\n",
diff --git a/src/message/mod.rs b/src/message/mod.rs
index 67640bf..e09a074 100644
--- a/src/message/mod.rs
+++ b/src/message/mod.rs
@@ -22,7 +22,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
-//!     .body("Be happy!")?;
+//!     .body(String::from("Be happy!"))?;
 //! # Ok(())
 //! # }
 //! ```
@@ -184,7 +184,7 @@
 //!
 //! ```
 
-pub use body::Body;
+pub use body::{Body, IntoBody, MaybeString};
 pub use mailbox::*;
 pub use mimebody::*;
 
@@ -196,13 +196,16 @@ mod mailbox;
 mod mimebody;
 mod utf8_b;
 
+use std::convert::TryFrom;
+use std::time::SystemTime;
+
+use uuid::Uuid;
+
 use crate::{
     address::Envelope,
-    message::header::{EmailDate, Header, Headers, MailboxesHeader},
+    message::header::{ContentTransferEncoding, EmailDate, Header, Headers, MailboxesHeader},
     Error as EmailError,
 };
-use std::{convert::TryFrom, time::SystemTime};
-use uuid::Uuid;
 
 const DEFAULT_MESSAGE_ID_DOMAIN: &str = "localhost";
 
@@ -410,23 +413,17 @@ impl MessageBuilder {
         })
     }
 
-    // In theory having a body is optional
-
-    /// Plain US-ASCII body
+    /// Create [`Message`] using a [`Vec<u8>`], [`String`], or [`Body`] body
     ///
-    /// Fails if is contains non ASCII characters or if it
-    /// contains lines longer than 1000 characters, including
-    /// the `\n` character.
-    ///
-    /// *WARNING*: Generally not what you want
-    pub fn body<T: Into<String>>(self, body: T) -> Result<Message, EmailError> {
-        let body = body.into();
+    /// Automatically gets encoded with `7bit`, `quoted-printable` or `base64`
+    /// `Content-Transfer-Encoding`, based on the most efficient and valid encoding
+    /// for `body`.
+    pub fn body<T: IntoBody>(mut self, body: T) -> Result<Message, EmailError> {
+        let maybe_encoding = self.headers.get::<ContentTransferEncoding>().copied();
+        let body = body.into_body(maybe_encoding);
 
-        if !self::body::is_7bit_encoded(body.as_ref()) {
-            return Err(EmailError::NonAsciiChars);
-        }
-
-        self.build(MessageBody::Raw(body))
+        self.headers.set(body.encoding());
+        self.build(MessageBody::Raw(body.into_vec()))
     }
 
     /// Create message using mime body ([`MultiPart`][self::MultiPart])
@@ -451,7 +448,7 @@ pub struct Message {
 #[derive(Clone, Debug)]
 enum MessageBody {
     Mime(Part),
-    Raw(String),
+    Raw(Vec<u8>),
 }
 
 impl Message {
@@ -485,7 +482,7 @@ impl EmailFormat for Message {
             MessageBody::Mime(p) => p.format(out),
             MessageBody::Raw(r) => {
                 out.extend_from_slice(b"\r\n");
-                out.extend(r.as_bytes())
+                out.extend_from_slice(&r)
             }
         }
     }
@@ -503,7 +500,9 @@ mod test {
 
     #[test]
     fn email_missing_originator() {
-        assert!(Message::builder().body("Happy new year!").is_err());
+        assert!(Message::builder()
+            .body(String::from("Happy new year!"))
+            .is_err());
     }
 
     #[test]
@@ -511,7 +510,7 @@ mod test {
         assert!(Message::builder()
             .from("NoBody <nobody@domain.tld>".parse().unwrap())
             .to("NoBody <nobody@domain.tld>".parse().unwrap())
-            .body("Happy new year!")
+            .body(String::from("Happy new year!"))
             .is_ok());
     }
 
@@ -520,7 +519,7 @@ mod test {
         assert!(Message::builder()
             .from("NoBody <nobody@domain.tld>".parse().unwrap())
             .from("AnyBody <anybody@domain.tld>".parse().unwrap())
-            .body("Happy new year!")
+            .body(String::from("Happy new year!"))
             .is_err());
     }
 
@@ -541,7 +540,7 @@ mod test {
                 vec!["Pony O.P. <pony@domain.tld>".parse().unwrap()].into(),
             ))
             .header(header::Subject("яңа ел белән!".into()))
-            .body("Happy new year!")
+            .body(String::from("Happy new year!"))
             .unwrap();
 
         assert_eq!(
@@ -551,6 +550,7 @@ mod test {
                 "From: =?utf-8?b?0JrQsNC4?= <kayo@example.com>\r\n",
                 "To: Pony O.P. <pony@domain.tld>\r\n",
                 "Subject: =?utf-8?b?0Y/So9CwINC10Lsg0LHQtdC705nQvSE=?=\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n",
                 "\r\n",
                 "Happy new year!"
             )
@@ -570,7 +570,7 @@ mod test {
             .multipart(
                 MultiPart::related()
                     .singlepart(
-                        SinglePart::eight_bit()
+                        SinglePart::builder()
                             .header(header::ContentType(
                                 "text/html; charset=utf8".parse().unwrap(),
                             ))
@@ -579,7 +579,7 @@ mod test {
                             )),
                     )
                     .singlepart(
-                        SinglePart::base64()
+                        SinglePart::builder()
                             .header(header::ContentType("image/png".parse().unwrap()))
                             .header(header::ContentDisposition {
                                 disposition: header::DispositionType::Inline,
diff --git a/src/transport/file/mod.rs b/src/transport/file/mod.rs
index 635c18b..f9ed1bb 100644
--- a/src/transport/file/mod.rs
+++ b/src/transport/file/mod.rs
@@ -19,7 +19,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
-//!     .body("Be happy!")?;
+//!     .body(String::from("Be happy!"))?;
 //!
 //! let result = sender.send(&email);
 //! assert!(result.is_ok());
@@ -51,7 +51,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
-//!     .body("Be happy!")?;
+//!     .body(String::from("Be happy!"))?;
 //!
 //! let result = sender.send(&email);
 //! assert!(result.is_ok());
@@ -79,7 +79,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
-//!     .body("Be happy!")?;
+//!     .body(String::from("Be happy!"))?;
 //!
 //! let result = sender.send(email).await;
 //! assert!(result.is_ok());
@@ -104,7 +104,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
-//!     .body("Be happy!")?;
+//!     .body(String::from("Be happy!"))?;
 //!
 //! let result = sender.send(email).await;
 //! assert!(result.is_ok());
diff --git a/src/transport/sendmail/mod.rs b/src/transport/sendmail/mod.rs
index ac9b57e..6cb377c 100644
--- a/src/transport/sendmail/mod.rs
+++ b/src/transport/sendmail/mod.rs
@@ -14,7 +14,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
-//!     .body("Be happy!")?;
+//!     .body(String::from("Be happy!"))?;
 //!
 //! let sender = SendmailTransport::new();
 //! let result = sender.send(&email);
@@ -40,7 +40,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
-//!     .body("Be happy!")?;
+//!     .body(String::from("Be happy!"))?;
 //!
 //! let sender = SendmailTransport::new();
 //! let result = sender.send(email).await;
@@ -63,7 +63,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
-//!     .body("Be happy!")?;
+//!     .body(String::from("Be happy!"))?;
 //!
 //! let sender = SendmailTransport::new();
 //! let result = sender.send(email).await;
diff --git a/src/transport/smtp/mod.rs b/src/transport/smtp/mod.rs
index 8320df1..ce577c2 100644
--- a/src/transport/smtp/mod.rs
+++ b/src/transport/smtp/mod.rs
@@ -40,7 +40,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
-//!     .body("Be happy!")?;
+//!     .body(String::from("Be happy!"))?;
 //!
 //! // Create TLS transport on port 465
 //! let sender = SmtpTransport::relay("smtp.example.com")
diff --git a/src/transport/stub/mod.rs b/src/transport/stub/mod.rs
index 008aee9..0353d19 100644
--- a/src/transport/stub/mod.rs
+++ b/src/transport/stub/mod.rs
@@ -19,7 +19,7 @@
 //!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
 //!     .to("Hei <hei@domain.tld>".parse()?)
 //!     .subject("Happy new year")
-//!     .body("Be happy!")?;
+//!     .body(String::from("Be happy!"))?;
 //!
 //! let mut sender = StubTransport::new_ok();
 //! let result = sender.send(&email);
diff --git a/testdata/email_with_png.eml b/testdata/email_with_png.eml
index a300e17..56734ea 100644
--- a/testdata/email_with_png.eml
+++ b/testdata/email_with_png.eml
@@ -7,15 +7,15 @@ MIME-Version: 1.0
 Content-Type: multipart/related; boundary="kve7WTqtIDDNFzED8Dccv2dHCJYXcEwETTAaIYCAcfn6lxvHldUc21nczexPKCfoDVec"
 
 --kve7WTqtIDDNFzED8Dccv2dHCJYXcEwETTAaIYCAcfn6lxvHldUc21nczexPKCfoDVec
-Content-Transfer-Encoding: 8bit
 Content-Type: text/html; charset=utf8
+Content-Transfer-Encoding: 7bit
 
 <p><b>Hello</b>, <i>world</i>! <img src=cid:123></p>
 --kve7WTqtIDDNFzED8Dccv2dHCJYXcEwETTAaIYCAcfn6lxvHldUc21nczexPKCfoDVec
-Content-Transfer-Encoding: base64
 Content-Type: image/png
 Content-Disposition: inline
 Content-ID: <123>
+Content-Transfer-Encoding: base64
 
 iVBORw0KGgoAAAANSUhEUgAAA+gAAAPoCAYAAABNo9TkAAAACXBIWXMAASdGAAEnRgHWSSfaAAAA
 GXRFWHRTb2Z0d2FyZQB3d3cuaW5rc2NhcGUub3Jnm+48GgAAIABJREFUeJzs3WmMlfXd//HvzLAO
diff --git a/tests/transport_file.rs b/tests/transport_file.rs
index 9b01850..f0996cb 100644
--- a/tests/transport_file.rs
+++ b/tests/transport_file.rs
@@ -20,7 +20,7 @@ mod test {
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
             .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
 
         let result = sender.send(&email);
@@ -31,7 +31,17 @@ mod test {
 
         assert_eq!(
             eml,
-            "From: NoBody <nobody@domain.tld>\r\nReply-To: Yuin <yuin@domain.tld>\r\nTo: Hei <hei@domain.tld>\r\nSubject: Happy new year\r\nDate: Tue, 15 Nov 1994 08:12:31 GMT\r\n\r\nBe happy!");
+            concat!(
+                "From: NoBody <nobody@domain.tld>\r\n",
+                "Reply-To: Yuin <yuin@domain.tld>\r\n",
+                "To: Hei <hei@domain.tld>\r\n",
+                "Subject: Happy new year\r\n",
+                "Date: Tue, 15 Nov 1994 08:12:31 GMT\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n",
+                "\r\n",
+                "Be happy!"
+            )
+        );
         remove_file(eml_file).unwrap();
     }
 
@@ -46,7 +56,7 @@ mod test {
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
             .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
 
         let result = sender.send(&email);
@@ -60,7 +70,17 @@ mod test {
 
         assert_eq!(
             eml,
-            "From: NoBody <nobody@domain.tld>\r\nReply-To: Yuin <yuin@domain.tld>\r\nTo: Hei <hei@domain.tld>\r\nSubject: Happy new year\r\nDate: Tue, 15 Nov 1994 08:12:31 GMT\r\n\r\nBe happy!");
+            concat!(
+                "From: NoBody <nobody@domain.tld>\r\n",
+                "Reply-To: Yuin <yuin@domain.tld>\r\n",
+                "To: Hei <hei@domain.tld>\r\n",
+                "Subject: Happy new year\r\n",
+                "Date: Tue, 15 Nov 1994 08:12:31 GMT\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n",
+                "\r\n",
+                "Be happy!"
+            )
+        );
         remove_file(eml_file).unwrap();
 
         assert_eq!(
@@ -82,7 +102,7 @@ mod test {
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
             .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
 
         let result = sender.send(email).await;
@@ -93,7 +113,17 @@ mod test {
 
         assert_eq!(
             eml,
-            "From: NoBody <nobody@domain.tld>\r\nReply-To: Yuin <yuin@domain.tld>\r\nTo: Hei <hei@domain.tld>\r\nSubject: Happy new year\r\nDate: Tue, 15 Nov 1994 08:12:31 GMT\r\n\r\nBe happy!");
+            concat!(
+                "From: NoBody <nobody@domain.tld>\r\n",
+                "Reply-To: Yuin <yuin@domain.tld>\r\n",
+                "To: Hei <hei@domain.tld>\r\n",
+                "Subject: Happy new year\r\n",
+                "Date: Tue, 15 Nov 1994 08:12:31 GMT\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n",
+                "\r\n",
+                "Be happy!"
+            )
+        );
         remove_file(eml_file).unwrap();
     }
 
@@ -109,7 +139,7 @@ mod test {
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
             .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
 
         let result = sender.send(email).await;
@@ -120,7 +150,17 @@ mod test {
 
         assert_eq!(
             eml,
-            "From: NoBody <nobody@domain.tld>\r\nReply-To: Yuin <yuin@domain.tld>\r\nTo: Hei <hei@domain.tld>\r\nSubject: Happy new year\r\nDate: Tue, 15 Nov 1994 08:12:31 GMT\r\n\r\nBe happy!");
+            concat!(
+                "From: NoBody <nobody@domain.tld>\r\n",
+                "Reply-To: Yuin <yuin@domain.tld>\r\n",
+                "To: Hei <hei@domain.tld>\r\n",
+                "Subject: Happy new year\r\n",
+                "Date: Tue, 15 Nov 1994 08:12:31 GMT\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n",
+                "\r\n",
+                "Be happy!"
+            )
+        );
         remove_file(eml_file).unwrap();
     }
 }
diff --git a/tests/transport_sendmail.rs b/tests/transport_sendmail.rs
index 99c68d3..15535c6 100644
--- a/tests/transport_sendmail.rs
+++ b/tests/transport_sendmail.rs
@@ -15,7 +15,7 @@ mod test {
             .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
 
         let result = sender.send(&email);
@@ -35,7 +35,7 @@ mod test {
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
             .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
 
         let result = sender.send(email).await;
@@ -54,7 +54,7 @@ mod test {
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
             .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
 
         let result = sender.send(email).await;
diff --git a/tests/transport_smtp.rs b/tests/transport_smtp.rs
index 49620d4..bcfaa41 100644
--- a/tests/transport_smtp.rs
+++ b/tests/transport_smtp.rs
@@ -10,7 +10,7 @@ mod test {
             .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
         SmtpTransport::builder_dangerous("127.0.0.1")
             .port(2525)
diff --git a/tests/transport_stub.rs b/tests/transport_stub.rs
index 01691fa..2266f00 100644
--- a/tests/transport_stub.rs
+++ b/tests/transport_stub.rs
@@ -16,7 +16,7 @@ mod test {
             .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
 
         sender_ok.send(&email).unwrap();
@@ -36,7 +36,7 @@ mod test {
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
             .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
 
         sender_ok.send(email.clone()).await.unwrap();
@@ -56,7 +56,7 @@ mod test {
             .to("Hei <hei@domain.tld>".parse().unwrap())
             .subject("Happy new year")
             .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body("Be happy!")
+            .body(String::from("Be happy!"))
             .unwrap();
 
         sender_ok.send(email.clone()).await.unwrap();