diff --git a/src/lib.rs b/src/lib.rs
index e193e2b..e9ab0ad 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -25,12 +25,11 @@ pub mod error;
 pub mod message;
 pub mod transport;
 
-pub use crate::address::Address;
 use crate::error::Error;
 #[cfg(feature = "builder")]
 pub use crate::message::{
     header::{self, Headers},
-    EmailFormat, Mailboxes, Message,
+    EmailFormat, Mailbox, Mailboxes, Message,
 };
 #[cfg(feature = "file-transport")]
 pub use crate::transport::file::FileTransport;
@@ -42,11 +41,10 @@ pub use crate::transport::smtp::client::net::TlsParameters;
 pub use crate::transport::smtp::r2d2::SmtpConnectionManager;
 #[cfg(feature = "smtp-transport")]
 pub use crate::transport::smtp::{SmtpTransport, Tls};
-pub use crate::transport::stub::StubTransport;
+pub use crate::{address::Address, transport::stub::StubTransport};
 #[cfg(feature = "builder")]
 use std::convert::TryFrom;
-use std::error::Error as StdError;
-use std::fmt;
+use std::{error::Error as StdError, fmt};
 
 /// Simple email envelope representation
 ///
@@ -92,9 +90,15 @@ impl TryFrom<&Headers> for Envelope {
         let from = match headers.get::<header::Sender>() {
             // If there is a Sender, use it
             Some(header::Sender(a)) => Some(a.email.clone()),
-            // ... else use the first From address
+            // ... else try From
             None => match headers.get::<header::From>() {
-                Some(header::From(ref a)) => Some(a.iter().next().unwrap().email.clone()),
+                Some(header::From(a)) => {
+                    let from: Vec<Mailbox> = a.clone().into();
+                    if from.len() > 1 {
+                        return Err(Error::TooManyFrom);
+                    }
+                    Some(from[0].email.clone())
+                }
                 None => None,
             },
         };
diff --git a/src/message/mod.rs b/src/message/mod.rs
index 062dc5b..cfc8d50 100644
--- a/src/message/mod.rs
+++ b/src/message/mod.rs
@@ -364,25 +364,32 @@ impl MessageBuilder {
         self
     }
 
-    fn insert_missing_headers(self) -> Self {
-        let mut new = self;
-
-        // Insert Date if missing
-        new = if new.headers.get::<header::Date>().is_none() {
-            new.date_now()
-        } else {
-            new
-        };
-
-        // TODO insert sender if needed?
-        new
-    }
-
     // TODO: High-level methods for attachments and embedded files
 
     /// Create message from body
     fn build(self, body: Body) -> Result<Message, EmailError> {
-        let res = self.insert_missing_headers();
+        // Check for missing required headers
+        // https://tools.ietf.org/html/rfc5322#section-3.6
+
+        // Insert Date if missing
+        let res = if self.headers.get::<header::Date>().is_none() {
+            self.date_now()
+        } else {
+            self
+        };
+
+        // Fail is missing correct originator (Sender or From)
+        match res.headers.get::<header::From>() {
+            Some(header::From(f)) => {
+                let from: Vec<Mailbox> = f.clone().into();
+                if from.len() > 1 && res.headers.get::<header::Sender>().is_none() {
+                    return Err(EmailError::TooManyFrom);
+                }
+            }
+            None => {
+                return Err(EmailError::MissingFrom);
+            }
+        }
 
         let envelope = match res.envelope {
             Some(e) => e,
@@ -485,6 +492,29 @@ impl Default for MessageBuilder {
 mod test {
     use crate::message::{header, mailbox::Mailbox, Message};
 
+    #[test]
+    fn email_missing_originator() {
+        assert!(Message::builder().body("Happy new year!").is_err());
+    }
+
+    #[test]
+    fn email_miminal_message() {
+        assert!(Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .to("NoBody <nobody@domain.tld>".parse().unwrap())
+            .body("Happy new year!")
+            .is_ok());
+    }
+
+    #[test]
+    fn email_missing_sender() {
+        assert!(Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .from("AnyBody <anybody@domain.tld>".parse().unwrap())
+            .body("Happy new year!")
+            .is_err());
+    }
+
     #[test]
     fn email_message() {
         let date = "Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap();
diff --git a/src/transport/stub/mod.rs b/src/transport/stub/mod.rs
index 0fbd7e8..3419b5d 100644
--- a/src/transport/stub/mod.rs
+++ b/src/transport/stub/mod.rs
@@ -23,8 +23,7 @@
 //! ```
 
 use crate::{Envelope, Transport};
-use std::error::Error as StdError;
-use std::fmt;
+use std::{error::Error as StdError, fmt};
 
 #[derive(Debug, Copy, Clone)]
 pub struct Error;