Issue with outgoing port 25 on Azure

[vamsiduranc]

Describe the bug

I am trying to setup postal smtp server in Azure VM for sending email from our own application.
But Postal connects to external mail servers (like Gmail, Yahoo, etc.) on port 25 and Azure VM is blocking outbound port 25, Postal is failing to deliver mail directly to recipient mail servers.

Expected behaviour

I want to use postal as smtp relay to send email from my application.
Monitor the mails from postal gui.

Is there any setting in postal.yml configuration that i can force postal server to use 587 to connect to the external email servers? please let me know.

Environment details

• OS: Ubuntu 22.04
• Type [Azure VM Server]

Additional information/context

below is the log snipet for reference

smtp-1    | 2025-06-25 14:51:09 +0000 DEBUG  Client identified as 183.82.xx.xxx trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:09 +0000 DEBUG  <= EHLO xxx-130 trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:09 +0000 DEBUG  => 250-My capabilities are trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:09 +0000 DEBUG  => 250 AUTH CRAM-MD5 PLAIN LOGIN trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:09 +0000 DEBUG  <= AUTH LOGIN trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:09 +0000 DEBUG  => 334 VXNlcm5hbWU6 trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:09 +0000 DEBUG  <= Y3Jvbi1lbWFpbHM= trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:09 +0000 DEBUG  => 334 UGFzc3dvcmQ6 trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:09 +0000 DEBUG  <= [redacted] trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:10 +0000 DEBUG  => 235 Granted for cron-emails/cron-emails trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:10 +0000 DEBUG  <= MAIL FROM:<abc@xxx-130> trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:10 +0000 DEBUG  => 250 OK trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:10 +0000 DEBUG  <= RCPT TO:<[email protected]> trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:10 +0000 DEBUG  Added external address '[email protected]' trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:10 +0000 DEBUG  => 250 OK trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:10 +0000 DEBUG  <= DATA trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:10 +0000 DEBUG  => 354 Go ahead trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:10 +0000 DEBUG  <= Received: by xxx-130 (sSMTP sendmail emulation); Wed, 25 Jun 2025 20:21:09 +0530 trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:10 +0000 DEBUG  Not logging further message data. trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:11 +0000 DEBUG  => 250 OK trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:11 +0000 DEBUG  <= QUIT trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:11 +0000 DEBUG  => 221 Closing Connection trace_id=OXQJVADY component=smtp-server
smtp-1    | 2025-06-25 14:51:11 +0000 DEBUG  Connection closed trace_id=OXQJVADY component=smtp-server
worker-1  | 2025-06-25 14:51:13 +0000 INFO   starting message unqueue component=worker thread=work0 original_queued_message=8
worker-1  | 2025-06-25 14:51:13 +0000 INFO   queue latency is 2.2943389415740967s component=worker thread=work0 original_queued_message=8
worker-1  | 2025-06-25 14:51:13 +0000 INFO   found 0 associated messages to process at the same time batch_key=outgoing-gmail.com component=worker thread=work0 original_queued_message=8
worker-1  | 2025-06-25 14:51:13 +0000 INFO   parsing message content as it hasn't been parsed before component=worker thread=work0 original_queued_message=8 queued_message=8
worker-1  | 2025-06-25 14:51:13 +0000 ERROR  Cannot connect to 2404:6800:4003:c11::1b:25 (gmail-smtp-in.l.google.com) (Errno::ENETUNREACH: Network is unreachable - connect(2) for "2404:6800:4003:c11::1b" port 25) log_id=LHA1F9RA component=worker thread=work0 original_queued_message=8 queued_message=8

[SpookOz]

I'm not the project owner. Just another user. But I'm pretty sure MTAs delivering email to other domains must use port 25, as defined in RFC 5321. Port 587 is only for SMTP Submission (with STARTTLS) from mail clients (MUAs).

You may need to use a VPS provider that allows port 25 outgoing.

[willpower232]

If azure doesn't want you to send emails directly from your servers then there isn't much you can do apart from try a different server provider. I'm sure there are plenty that do if you can't ask azure to allow emails.