After many attempts to fix the problems with sending emails to Microsoft domains (Outlook, Hotmail, Live, etc), every communication with them went some like this;
I get the following error when trying to send email to an @live.com user.
"SMTP error from remote mail server after pipelined MAIL FROM:<*> SIZE=17884: 550 5.7.1 Unfortunately, messages from [*.*.*.*] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors."
I double checked all mail server settings, and related DNS entries, all SPF, DKIM, and PTR records also check out. Can I have my IP address removed?
Your IP address isn't on our blocklist and we don't see anything stopping you from sending us emails, please read https://sendersupport.olc.protection.outlook.com/pm/troubleshooting.aspx.
The error message from your computer very clearly says my IP address is on your block list. Here's the message again;
"SMTP error from remote mail server after pipelined MAIL FROM:<*> SIZE=17884: 550 5.7.1 Unfortunately, messages from [*.*.*.*] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150)."
I contacted my host and we doubled checked all of our settings. If my IP address isn't on your block list, then why does your server incorrectly say it is?
Nothing is wrong! Ticket is now closed.
I did all this about three times over the last few weeks, and the results were always the same, nothing is wrong.
So after speaking with our hosting provider again a few days ago, they submitted a request to Microsoft to have the entire IP address range removed. I'm still waiting to hear back the result on this, but hopefully they will have more success then I did.
In the mean time, I've been manually approving registrations with Microsoft email addresses but we might just have to not accept any Microsoft email addresses for members on this website (Microsoft is evil, this might not be a bad thing).