You may remember that Microsoft domains (,,, and were refusing all e-mail coming from my server. This is not as deadly as Gmail refusing to talk to you (as Gmail currently hosts about 50% of my contacts), but it’s still a pretty big deal.

Their servers would always reject my e-mail with this error:

2017-06-10 18:48:29 1dJlQy-0007SD-Fk ** R=dnslookup T=remote_smtp X=TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256 DN="CN=*": SMTP error from remote mail server after MAIL FROM:<> SIZE=1814: host []: 550 SC-001 (SNT004-MC1F14) Unfortunately, messages from 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

Setting up DKIM on top of SPF that I already had did not help.

I finally ran into an explanation: Microsoft basically refuses e-mail coming from any new server. I think I’d been sending e-mail from that IP for a while, but apparently that wasn’t enough. The article points to a secret form on Microsoft’s support Web site, which lets you beg them to consider de-blacklisting your IP address. Apparently it works, so I can finally send e-mail to the 10% or so of my friends who are hosted by them.

I guess the next step is for Microsoft, Gmail and the couple of very large e-mail providers to just stop talking to any small server.