diff --git a/email.go b/email.go
index 3b4efb2..9512704 100644
--- a/email.go
+++ b/email.go
@@ -82,6 +82,11 @@ func sendSMTPEmail(to, cc, bcc []string, from, subject, body string, attachments
 		}
 	}
 
+	// If no authentication is provided, disable it for internal mail relays
+	if server.Username == "" && server.Password == "" {
+		server.Authentication = mail.AuthNone
+	}
+
 	switch strings.ToLower(smtpEncryption) {
 	case "ssl":
 		server.Encryption = mail.EncryptionSSLTLS
diff --git a/main.go b/main.go
index a820b78..d744882 100644
--- a/main.go
+++ b/main.go
@@ -85,6 +85,9 @@ var rootCmd = &cobra.Command{
 			if from == "" {
 				from = smtpUsername
 			}
+		case smtpHost != "":
+			// Allow SMTP delivery with just host for internal mail relays (no auth)
+			deliveryMethod = SMTP
 		}
 
 		switch deliveryMethod {