SMTP sending errors are ignored

[Björn Jacke]

When the smtp server does not accept a message that mailman tried to send via smtp, the error is being ignored by mailman.

In my specific case I reject mails at the MTA based on whether or not the recipient domain is on a blacklist. If someone with a blacklisted domain wants to subscribe via the mailman web interface he sees no error message, just the usual "Your subscription request has been received...".

What I would expect is that mailman notices that the SMTP delevery failed and that the user gets back some kind of error message about a failure.

[Mark Sapiro (msapiro)]

Mailman does see the failure. It is logged in Mailman's smtp-failure log and depending on the situation may be recorded as a bounce for the user, but in the case of a subscription confirmation request, the recipient isn't yet a list member so a bounce can't be recorded.

The underlying issue is that the SMTP reject is of a message From Mailman so it is Mailman that sees the reject. There's nothing Mailman can do at this point to inform the user, since even if Mailman tried, whatever Mailman tried to send to the user would also be rejected by the MTA.

Since the original request comes from the web, there's not much you can do. If you the blacklisted domains are a static list, you could add

^.*[@.]bad.domain.tld

for each domain to the list's ban_list.

Or, you could set up a separate SMTP submission port other than 25 in your MTA for Mailman to use and not apply blacklisting to mail submitted there.

[Björn Jacke (bjoern-j3e)]

i was specifically talking about subscription by web interface (not by subscription mail), which is the most common way if users to subscribe at our site.

the web interface can see the result of the smtp delivery to mailman and it would be able to give back negative feedback to the user accordingly.

[Mark Sapiro (msapiro)]

No. The web subscribe UI cannot see the result of the smtp delivery attempt. This delivery is done by a completely asynchronous process that has no way to communicate results back to the web subscribe process.