Post #1124355
2026-04-13 06:43 UTC
Replies (1)
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@michael@westergaard.social 2026-04-13 08:00
Exchange is not the issue (for that). The issue is they are very strict and it's very hard to not get on their shitlist. In addition to SPF, DKIM, and DMARC, which are all mandatory these days, you need to make sure that your IP is not on a blacklist (and most cheap cloud providers that allow port 25 traffic are), and that your domain isn't (if you sent mails with invalid DMARC/SPF/DKIM or you don't have DMARC in a strict mode and somebody used your domain to send spam, it is on a blacklist). They often employ graylisting (deny mails the first time around, only accepting on re-send) and nebulous anti-spam rules (proprietary SpamAssassin-like checks – nebulous to prevent spammers from working around them). It's hard, very hard, to run a working mail server. It makes the 90s/00s with sendmail config woes seem nice in comparison. You cannot just boot up a Postfix and expect to be able to send mail. For the most part, this is fair. Each of the rules is there to prevent spam and makes sense. The unfortunate fact is that it simultaneously makes it very hard for self-hosters/small companies to send legitimate mail. Because their mail looks exactly like spam. I had a domain blacklisted at Google due to slightly wrong DMARC + DKIM setting; took a good 2 weeks to get it removed despite all checks saying it was fine. mxtoolbox is only the beginning (it found no issue with my blacklisted domain); mail-tester is better, being on Google Postmaster is a must, and a DMARC monitor is close to a necessity. BIMI often helps because it's so extremely expensive.