The postfix manpage says you can specify an action for
unverified_recipient_tempfail_action. But I can't specify
fatal: bad configuration: unverified_recipient_tempfail_action = permit
So my only options are reject, defer or defer_if_permit?
I use recipient address verification for my fallback MX server, which should not defer incoming mails (because if I want incoming mails to be deferred in case the primary goes down, I wouldn't have a backup MX at all, so that the messages are deferred at the incoming SMTP server).
But now, when the verify-cache has expired or the cache doesn't have an entry yet for the user in question, it will defer the request, defeating the purpose of a backup MX server.
So how do I make it so that when the primary goes down, it will accept all mail?
I should add that this mail server also acts as the incoming mail server for a web hosting server managed by Plesk (control panel). Plesk doesn't have spam filtering (except for extra cost), so I set up another virtual machine that does the incoming mail and spam filtering for that host. I use recipient address verification to avoid the mailqueue filling up with bounce mails (and to properly reject the request when the user does not exist, and not accept and bounce later, avoiding backscatter mail).
But I also want to use that incoming mail server as backup MX for certain domains (using the
relay transport to avoid delivery loops). I guess for those domains, I don't need reject_unverified_recipient. Would it be enough to insert
On the other hand, I still think it makes sense to use recipient address verification during periods the primary host is not down: this avoids backscatter mail (mail bounced to (fake) senders because of spam sent to non-existing users).
In any case, for either use of the incoming mail server, it is not possible to create recipient maps. One reason is that users create e-mail addresses dynamically on the Plesk machine and the other is that the domains for which we are backup MX are not under our control, so we don't know which users there are.