Turns out software is the easy part, IP reputation is the boss.
Context: I’ve set up a mail server on VPS and it’s pretty tiring to deal with the mail server blocking my mail.
GMail is really lenient, you just need to pass DKIM/SPF, and they will tell you what’s wrong and that’s logged in your MTA logs.
Apple iCloud however, even though you go through the Proofpoint IP unlisting, if there’s still a blocker, you will have to contact their postmaster team, this step is NOT optional if the mail keep getting bounced from their server.
Microsoft Outlook won’t even tell you the mail is blocked, their mail server will return a success to MTA (and say it’s queued) even though it will go right into a black hole.
You’ll have to get into their system to delist, but after that it’s gucci:
https://sender.office.com
Yahoo mail, at least it goes into spam.
There are probably more but i cba to read through all of them, if you know more please comment.
Other useful links:
https://postmaster.google.com/v2/sender_compliance
https://sendersupport.olc.protection.outlook.com/snds
https://senders.yahooinc.com/
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