Using SMTP2GO as a failover.

[dojoca]

I'm having an odd problem and have nearly torn my hair out trying to get this to work.

Issue: I want to send emails directly using the MX resolver. My IP is, for some reason, listed in Trend Micro's banned IP list. All other email works fine, including to gmail/yahoo/outlook/etc.

What I want: I have set up an SMTP2GO account. If I route all email via SMTP2GO, it works fine.

But, I'd rather have Stalwart first try to deliver emails using the MX-based send, and if that fails (permanently - giving code 550) then I want it to then rather send the email via SMTP2GO.

I've tried so many different expressions. Any idea how I can achieve this?

Current config:

Under Settings > SMTP > Outbound > Strategies in the GUI. (I have SMTP2Go set up as smtp-alt).

IF: is_local_domain('*', rcpt_domain) then: 'local'
IF: last_error == 'unexpected-reply' && last_status == 550 then: 'smtp-alt'
'mx'

Am I doing something wrong here with the syntax?

Edited to add - this is the message I get when my mail gets rejected:

[email protected] (host 'host.in.tmes-anz.trendmicro.com' rejected command 'RCPT TO:[email protected]' with code 550 (5.7.1) '[email protected]: Recipient address rejected: Mail from <MY_IP_ADDRESS> was refused due to the sender IP found in ERS-DUL. For details, query the IP reputation on https://servicecentral.trendmicro.com/en-US/ers/.')

[mdecimus]

Hi, the issue is that 5xx is a permanent error so delivery won't be reattempted.

[dojoca]

Ahh yep thanks.

Is there a different way to achieve this though?

[mdecimus]

If you know the domain names that require delivery over SMTP2GO you could create a routing rule for these.