Same bug family as the mail-DNS fix from earlier that day, found while checking that fix live on a split mail and web install: the Email Deliverability page’s reverse-DNS (PTR) check was fixed to Main’s own IP, on both the admin and account-side versions of the page.
That is correct when mail and web share a box, but wrong once a linked Mail Only satellite is switched on. A receiving mail server checks the sending server’s reverse DNS, not the website’s, so the page was showing Main’s result where mail goes out through a different server.
Both controllers now resolve the IP through the same active-mail-server lookup the earlier MX fix uses, so the PTR check follows wherever mail is actually sent from. It is a good reminder that “the fix works” and “everything downstream of the old assumption got fixed too” are not the same claim. Tested (2504/2504) and live-verified.