diff --git a/lettre/src/sendmail/mod.rs b/lettre/src/sendmail/mod.rs
index 6437f42..edb669b 100644
--- a/lettre/src/sendmail/mod.rs
+++ b/lettre/src/sendmail/mod.rs
@@ -52,6 +52,7 @@ impl<'a, T: Read + 'a> EmailTransport<'a, T, SendmailResult> for SendmailTranspo
                     "-i",
                     "-f",
                     &email.from().to_string(),
+                    "--",
                     &to_addresses.join(" "),
                 ],
             )