http://www.mydigitallife.info/how-to-remove-server-ip-address-from-msn-hotmail-block-blacklist/
https://mail.live.com/mail/troubleshooting.aspx#Codes
Another challenge with maintaining a mail server is keeping your server off
of the various blacklists, also known as DNSBL, blocklists, or blackhole
lists. These lists contain the IP addresses of mail servers that were
reported to send spam or junk mail or for having improperly configured DNS
records
https://www.digitalocean.com/community/tutorials/why-you-may-not-want-to-run-your-own-mail-server
