diff --git a/src/mimefactory.rs b/src/mimefactory.rs
index 2c6a56842..4e957c58c 100644
--- a/src/mimefactory.rs
+++ b/src/mimefactory.rs
@@ -368,7 +368,7 @@ impl<'a, 'b> MimeFactory<'a, 'b> {
             self.from_addr.clone(),
         );
 
-        let mut to = Vec::with_capacity(self.recipients.len());
+        let mut to = Vec::new();
         for (name, addr) in self.recipients.iter() {
             if name.is_empty() {
                 to.push(Address::new_mailbox(addr.clone()));
@@ -380,6 +380,10 @@ impl<'a, 'b> MimeFactory<'a, 'b> {
             }
         }
 
+        if to.is_empty() {
+            to.push(from.clone());
+        }
+
         if !self.references.is_empty() {
             unprotected_headers.push(Header::new("References".into(), self.references.clone()));
         }