SMTP Error 550 when sending from v28.4

[sayem314]

I am experiencing a regression with SMTP sending after upgrading to v28.4. This configuration was working perfectly last month on a previous version (likely v28.3), and no changes have been made to the SMTP credentials, host, or environment variables. The server is now returning a 550 error during the RCPT TO command.

The issue appears specific to the application's SMTP handling. I have verified that the exact same credentials and sender identity work without issue in Roundcube from the same host. Network connectivity checks from within the container confirm the SMTP host is reachable on port 587.

The error log indicates the failure occurs during the SMTP RCPT TO phase. This suggests that something in the way v28.4 handles the SMTP handshake or the construction of envelope-from headers is now triggering the provider's outbound filters. Since the setup was stable before the update, it seems like a change in the internal mailer logic is the cause.

{
  "level": "error",
  "error": "failed to send magic code email: send failed: sending SMTP RCPT TO command: 550 Intentionally vague error message requiring you to contact support",
  "message": "Failed to send magic code"
}

[sayem314]

I confirmed that manually setting SMTP_EHLO_HOSTNAME=xxx.com in my environment variables resolved the 550 error.

The issue was introduced by commit 0abedd7. Strict providers like MxRoute reject the default localhost or container ID used in the SMTP handshake.

To prevent this for other users, the application should automatically parse the domain from the smtp_from_email setting and use it as the default EHLO hostname when SMTP_EHLO_HOSTNAME isn't explicitly defined.

[pierre-b]

Thanks for the idea, improved in https://github.com/Notifuse/notifuse/releases/tag/v29.0 !