diff --git a/src/message/mimebody.rs b/src/message/mimebody.rs
index a2265d0..bb61e48 100644
--- a/src/message/mimebody.rs
+++ b/src/message/mimebody.rs
@@ -1,3 +1,5 @@
+use std::io::Write;
+
 use crate::message::{
     header::{ContentTransferEncoding, ContentType, Header, Headers},
     EmailFormat, IntoBody,
@@ -132,7 +134,8 @@ impl SinglePart {
 
 impl EmailFormat for SinglePart {
     fn format(&self, out: &mut Vec<u8>) {
-        out.extend_from_slice(self.headers.to_string().as_bytes());
+        write!(out, "{}", self.headers)
+            .expect("A Write implementation panicked while formatting headers");
         out.extend_from_slice(b"\r\n");
         out.extend_from_slice(&self.body);
         out.extend_from_slice(b"\r\n");
@@ -390,7 +393,8 @@ impl MultiPart {
 
 impl EmailFormat for MultiPart {
     fn format(&self, out: &mut Vec<u8>) {
-        out.extend_from_slice(self.headers.to_string().as_bytes());
+        write!(out, "{}", self.headers)
+            .expect("A Write implementation panicked while formatting headers");
         out.extend_from_slice(b"\r\n");
 
         let boundary = self.boundary();
diff --git a/src/message/mod.rs b/src/message/mod.rs
index 670d8e6..dcfa09c 100644
--- a/src/message/mod.rs
+++ b/src/message/mod.rs
@@ -250,7 +250,7 @@ mod mailbox;
 mod mimebody;
 mod utf8_b;
 
-use std::{convert::TryFrom, time::SystemTime};
+use std::{convert::TryFrom, io::Write, time::SystemTime};
 
 use uuid::Uuid;
 
@@ -533,7 +533,8 @@ impl Message {
 
 impl EmailFormat for Message {
     fn format(&self, out: &mut Vec<u8>) {
-        out.extend_from_slice(self.headers.to_string().as_bytes());
+        write!(out, "{}", self.headers)
+            .expect("A Write implementation panicked while formatting headers");
 
         match &self.body {
             MessageBody::Mime(p) => p.format(out),