Blog posts dated February 2016 – 2 posts found:

HTTPS sites are encrypted with a public/private key pair, being vouched for in a certificate by having that certificate signed by a trusted CA. However, it might be possible that somebody generates a certificate for your domain and has it signed by a fraudulent or compromised CA. Protection against this is provided by use of HKPK. But what keys should be "pinned" and why? I've found information about this online to be lacking, so I did some research and here's the results.

Microsoft's Outlook.com is one of the largest email providers in the world and anybody who sends email to customers will encounter plenty of outlook.com, hotmail.com or live.com addresses. As such, Microsoft has to deal with a lot of spam for all those billions of emails it processes and sometimes the spam detection is a bit overzealous. It doesn't take much for your server's IP address to be blacklisted, or you might even inherit a blacklisting from the previous owner of the IP address assigned to your newly commissioned server. Then you get the 550 SC-001 error.