Change: Rather than presuming a given domain has a well performing and functional MX, the default Postfix configuration will move to be more restrictive by default to better align with reality. An explicit opt-in will be available to well-performing high-volume domains. PM me if you think you qualify and you are the mail admin for your forum user’s domain.
Expected Impact: Emails from the forum may begin arriving more slowly, especially for domains with several users subscribed to the forum.
Reason: Mail server performance has been managed manually by scraping the Postfix logs, identifying slow destinations, and manually intervening to ensure the main queue performs well. This has historically worked fine as most domains have used standard O365 and Google MXes, but recently more domains have been moving away to poor performing servers. This causes backlogs on the main delivery queue until I have a chance to identify and intervene. The new configuration should be more consistent with performance, as it will allow for a wider default queue. Exceptionally poorly performing servers (like Mimecast, Barracuda, several shared webhosts and OATH) will continue to remain on a manually maintained list and slowly added back to the default delivery pool as I have a chance to confirm they don’t excessively impact everyone else.
As A Reminder: OATH (Yahoo, etc.) and Microsoft Consumer (Hotmail, etc) domains have exceedingly poor deliverability. This is a problem of the respective properties’ choice, so if you have problems, I recommend reaching out to them or changing your forum email to another address (happy to help and/or make recommendations).