diff --git a/smtp.mail.inc b/smtp.mail.inc
index a053187..d8fd2d2 100644
--- a/smtp.mail.inc
+++ b/smtp.mail.inc
@@ -228,6 +228,9 @@ class SmtpMailSystem implements MailSystemInterface {
           break;
 
         case 'return-path':
+          $mailer->Sender = $value;
+          break;
+
         case 'mime-version':
         case 'x-mailer':
           // Let PHPMailer specify these.