About Kevin's email [1] …
I was hesitant to talk about the problem I had in replying, because it's well known that the Big Players (Google and Microsoft in particular) don't really care about smaller email servers, making it difficult to self-host email.
Yet … the bounce message I recieved contained the following:
Diagnostic-Code: X-Postfix; host
hotmail-com.olc.protection.outlook.com[104.47.66.33] said: 550 5.7.1
Unfortunately, messages from [71.19.142.20] weren't sent. Please contact
your Internet service provider since part of their network is on our block
list (S3140). You can also refer your provider to
http://mail.live.com/mail/troubleshooting.aspx#errors.
[MW2NAM12FT105.eop-nam12.prod.protection.outlook.com
2023-10-29T06:59:01.371Z 08DBD7D7D4735644] (in reply to MAIL FROM command)
That link? Absolutely useless. To address the issue, I would have to sign in to my “Microsoft Account” or pay for services like this company [2] that “ensures” email delivery (which I'm reading as “pay to play”). And of course I'm a company, because who would be so silly as to run their own email server? Sheesh!
Why Microsoft couldn't just send a link to their Office 365 Anti-Spam IP Delist Portal [3] in the first place (which took entirely too long to find and didn't appear on the link they did send), I don't know—I guess that could make it too easy to “game” or something.
Mainly, I'm writing this for my future self to save some time when this happens again.
The bounce came from outlook.com, but Kevin's email address is from hotmail.com, and it's hotmail.com that has a block on my IP (Internet Protocol), not outlook.com.
I found that out because I followed the instructions on the “Office 365 Anti-Spam Delist Portal” and it said “Oh! You aren't blocked! Try this link!” with “this link” asking me to log into my “Microsoft Account.”
Seriously, Microsoft? XXXX you.
[2] https://www.validity.com/everest/sender-certification/
[3] https://sender.office.com/