diff --git a/src/mail.js b/src/mail.js
index 3e5b585b6..4f0450c4e 100644
--- a/src/mail.js
+++ b/src/mail.js
@@ -212,22 +212,25 @@ async function listDomains() {
     return results;
 }
 
-async function checkOutboundPort25() {
-    return await new Promise((resolve) => {
+async function checkOutboundPort25(family) {
+    const ip = family === 4 ? await network.getIPv4() : await network.getIPv6();
+    if (ip === null) return; // ipv4/ipv6 is disabled
+
+    return await new Promise((resolve, reject) => {
         const client = new net.Socket();
         client.setTimeout(5000);
-        client.connect({ port: 25, host: constants.PORT25_CHECK_SERVER, family: 4 }); // family is 4 to keep it predictable
+        client.connect({ port: 25, host: constants.PORT25_CHECK_SERVER, family }); // family is 4 to keep it predictable
         client.on('connect', function () {
             client.destroy(); // do not use end() because it still triggers timeout
-            resolve({ status: 'passed', message: 'Port 25 (outbound) is unblocked' });
+            resolve();
         });
         client.on('timeout', function () {
             client.destroy();
-            resolve({ status: 'failed', message: `Connect to ${constants.PORT25_CHECK_SERVER} timed out. Check if port 25 (outbound) is blocked` });
+            reject(new Error(`IPv${family} connect to ${constants.PORT25_CHECK_SERVER} timed out`));
         });
         client.on('error', function (error) {
             client.destroy();
-            resolve({ status: 'failed', message: `Connect to ${constants.PORT25_CHECK_SERVER} failed: ${error.message}. Check if port 25 (outbound) is blocked` });
+            reject(new Error(`IPv${family} connect to ${constants.PORT25_CHECK_SERVER} failed: ${error.message}`));
         });
     });
 }
@@ -236,7 +239,15 @@ async function checkSmtpRelay(relay) {
     assert.strictEqual(typeof relay, 'object');
 
     if (relay.provider === 'noop') return { status: 'skipped', message: 'Outbound disabled' };
-    if (relay.provider === 'cloudron-smtp') return await checkOutboundPort25();
+    if (relay.provider === 'cloudron-smtp') {
+        const results = await Promise.allSettled([ checkOutboundPort25(4), checkOutboundPort25(6) ]);
+        if (results[0].status === 'fulfilled' && results[1].status === 'fulfilled') return { status: 'passed', message: 'Port 25 (outbound) is unblocked' };
+        const messages = [];
+        if (results[0].status === 'rejected') messages.push(results[0].reason.message);
+        if (results[1].status === 'rejected') messages.push(results[1].reason.message);
+        messages.push('Check if port 25 (outbound) is blocked.');
+        return { status: 'failed', message: messages.join('. ') };
+    }
 
     const options = {
         connectionTimeout: 5000,