This standard specifies a single, reserved mailbox address (local-part) which is to be valid at each site. .. "Postmaster@domain" is required to be valid.
The latest bunch of losers are The Works, who send their marketing emails properly but not the rather more important order acknowledgement and - what I was missing - the 'it's ready to collect' ones: they're 'from' somewhere that doesn't match the IP address they're sent from. As that's what loads of spambots do, such email gets blocked by lots of places.
(The other annoying bunch are the ones who do the equally important 'here's your ticket' email for the local arts cinema. They ignore the 'MUST' in 'must retry' sending emails that get a 'not ready at the moment' message from the destination mail server.)
This entry was originally posted at http://lovingboth.dreamwidth.org/534147.html, because despite having a permanent account, I have had enough of LJ's current owners trying to be evil. Please comment there using OpenID - have and if you have an LJ account, you can use it for your OpenID account. Or just join Dreamwidth! It only took a couple of minutes to copy all my entries here to there.