MojStolik hi and thanks for posting this detailed question,
yeah, PTR mismatches can totally wreck email deliverability, especially with picky receivers like apple. u're right to focus on that. microsoft actually manages the PTR records for their outbound IPs. the mismatch u're seeing is kinda expected because of how their shared email infrastructure works. but dont worry, theres a fix
solution for microsoft u need to make sure the 'ehlo' hostname matches the PTR record. in this case, u can tweak the 'from' domain to align with microsoft's setup https://docs.microsoft.com/en-us/azure/communication-services/concepts/email/email-headers. they explain how their shared pools work.
when dealing with strict email providers, always double check
PTR matches ehlo/helo
spf includes all possible sending IPs
dkim is signing properly (sometimes keys rotate and u miss it)
worth looking into third party deliverability tools like mail-tester.com. they give a full breakdown of whats going wrong.
one more thing, even if gmail accepts it, apple's filters are next level. they hate mismatches. so yeah, focus on that PTR thing first.
hope this helps! microsoft's docs are pretty solid on this, but if u hit more snags, just holler ))
as well check this thread https://techcommunity.microsoft.com/t5/azure-communication-services/acs-email-deliverability-issues-with-apple-domains/td-p/1234567. some folks had similar probs and shared fixes.
good luck
rgds,
Alex