diff --git a/modules/rcart/mod.ts b/modules/rcart/mod.ts
index 6467fa5..e67a3d7 100644
--- a/modules/rcart/mod.ts
+++ b/modules/rcart/mod.ts
@@ -49,15 +49,21 @@ let _smtpTransport: Transporter | null = null;
 
 function getSmtpTransport(): Transporter | null {
 	if (_smtpTransport) return _smtpTransport;
-	if (!process.env.SMTP_PASS) return null;
+	const host = process.env.SMTP_HOST || "mail.rmail.online";
+	const isInternal = host.includes('mailcow') || host.includes('postfix');
+	if (!process.env.SMTP_PASS && !isInternal) return null;
+	// Internal mailcow network: relay on port 25 without auth
+	// External: use port 587 with STARTTLS + auth
 	_smtpTransport = createTransport({
-		host: process.env.SMTP_HOST || "mail.rmail.online",
-		port: Number(process.env.SMTP_PORT) || 587,
-		secure: Number(process.env.SMTP_PORT) === 465,
-		auth: {
-			user: process.env.SMTP_USER || "noreply@rmail.online",
-			pass: process.env.SMTP_PASS,
-		},
+		host,
+		port: isInternal ? 25 : (Number(process.env.SMTP_PORT) || 587),
+		secure: !isInternal && Number(process.env.SMTP_PORT) === 465,
+		...(isInternal ? {} : {
+			auth: {
+				user: process.env.SMTP_USER || "noreply@rmail.online",
+				pass: process.env.SMTP_PASS!,
+			},
+		}),
 		tls: { rejectUnauthorized: false },
 	});
 	return _smtpTransport;