diff --git a/smtp.go b/smtp.go
index 2aa49c8..01295a2 100644
--- a/smtp.go
+++ b/smtp.go
@@ -72,12 +72,17 @@ func (d *Dialer) Dial() (SendCloser, error) {
 		return nil, err
 	}
 
-	if d.LocalName != "" {
-		if err := c.Hello(d.LocalName); err != nil {
-			return nil, err
+	if d.LocalName == "" {
+		atIndex := strings.LastIndex(d.Username, "@")
+		if atIndex >= 0 {
+			d.LocalName = d.Username[atIndex+1:]
 		}
 	}
 
+	if err := c.Hello(d.LocalName); err != nil {
+		return nil, err
+	}
+
 	if !d.SSL {
 		if ok, _ := c.Extension("STARTTLS"); ok {
 			if err := c.StartTLS(d.tlsConfig()); err != nil {