I recently had the pleasure of being greeted by the following error message when sending e-mails to @live, @outlook, @hotmail, and related domains:
smtp; 550 SC-001 (SNT004-MC3F41) Unfortunately, messages from x.x.x.x weren't sent. Please contact your Internet service provider since part of their network is on our block list. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors.
As far as I knew, my dedicated IP address range was not listed on any public blacklists. The issue seemed very much isolated to Microsoft’s email servers.
After endless searching I came across the following support link for “Internet service Providers” to contact the Microsoft postmasters: https://support.microsoft.com/en-us/getsupport?oaspworkflow=start_22.214.171.124&wfname=capsub&productkey=edfsmsbl3&locale=en-us&ccsid=636033511358958563
Much to my surprise within only an hour or two of submitting my support request I received an replied via email. Ironically the email ended up in my spam folder under the following reason:
It has a from address in css.one.microsoft.com but has failed css.one.microsoft.com's required tests for authentication.
Nonetheless, their reply confirmed that my IP address range had been “conditionally mitigated” and upon testing the next morning, the error had gone.
All round thumbs up! Shame I had to write this article so it doesn’t take me 3 hours to find how to contact them in the future – in before the above link goes AWOL 🙁