New Code!
Postoffice has been pushed up to version 1.5.4-beta3 with a slight tweak to the milter interface that makes it properly handle milters that return 4xx (tempfail) statuses. It used to treat them as a permanent failure (and would defer them until after the DATA phase of a sendmail transaction) but now spits out the response immediately and ignores the single command that caused the temporary failure.
It’s a trivially small release and it won’t cause any explosions any larger than 1.5.4-beta2 did, so it’s just the New Code! to install on a lazy thanksgiving weekend.