Ladies and gentlemen, i present to you, Microsoft/Outlook blocklist S3140. This list blocks ALL NEW MAILSERVERS. ALL OF THEM. My personal mailserver can email gmail without issue, and yet microsoft says no.
<[person i was trying to email]>: host outlook-com.olc.protection.outlook.com[104.47.59.161] said: 550 5.7.1 Unfortunately, messages from [my mailserver IP] 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.com172.105.184.201/mail/troubleshooting.aspx#errors. [error code that might be user specific so i'm redacting it] (in reply to MAIL FROM command)