christoph ender's


saturday the 19th of august, 2023

working around microsoft blacklisting

Catching up on yesterday's post: It's hard to deny that self-hosting mail for individuals or smaller companies has become a much greater challenge nowadays.

Some references:

Especially regarding Microsoft, I've lately adapted a new way of rolling out mail servers: Get a new VM somewhere and immediately, before doing anything else, check the IP at Microsoft's “Smart Network Data Service” and/or telnet to one of their mail servers and try to get a mail delivered to an Exchange Online account. If the new machine's IP is blacklisted at SDNS or the test delivery results in the mail getting immediately dumped to the spam folder, just cancel the new VW and roll out a new one – this of course only makes sense when the VM is billed accordingly and costs are neglegible. I've never succeeded at having an IP unblocked by Microsoft without some human intervention on their part and they don't provide even the slightest information at all why some IP is on their blacklist – you'll just get a list of conditions you'll have to meet and an endless stream of “Not qualified for mitigation” messages. Just trying IPs until finding one that's not blocked saves a huge amount of time.