Microsoft is absolutely hell to deal with. Especially if you are hosted on Linode. They frequently ban entire linode subnets. I’ve had to resort to routing all send mail via Amazon AWS SES just because of Microsoft’s IP range bans. It’s not what I’m doing, but my neighbours.
It's funny because throughout Q1 2024 a huge range of Microsoft's own IP addresses were blacklisted by Spamcop and other blacklist providers spam/phishing attacks coming from outlook.com addresses. (Google "EX703958" (MS's issue#) for some fun reading.) They (and their enterprise customers) have been on the receiving end of the same thing they do to others.
Allegedly, Microsoft subscribes to random spam checklists like UCEProtect.
uceprotect bans entire subnets & ASNs if just one IP is suspected of sending spam.Apparently, you can pay to get your IP whitelisted for some time but it will be back on the list again. Its probably a scam/shakedown operation.
As these lists discourage self-hosting and benefit large email providers, they take their own time for fixing these issues.
