Microsoft keeps rejecting mail from our IP networks, affecting recipients at Outlook, Hotmail, Live and MSN. We have no influence on this: we can neither get the block lifted nor predict it.

What the error message looks like

<xyz@outlook.com>: host eur.olc.protection.outlook.com[104.47.14.33] said:
550 5.7.1 Unfortunately, messages from [51.89.85.77] 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.com/mail/troubleshooting.aspx#errors.

The IP address in square brackets is the server the mail came from, often our web hosting server.

Why this happens

Microsoft rates entire IP ranges and gives no specific reason. Whether one of our servers or networks gets through can change from week to week. This affects web hosting as well as vServers. Requests to Microsoft to lift the block go nowhere.

What we do

We monitor the situation as well as we can and inform you when system mails to known recipients are affected. For your own mails, however, we cannot change anything about the block.

What you can do

  • Use an external sender: Send mail to Microsoft addresses through a mail provider’s server (relay or smarthost) instead of directly from your server.
  • Another recipient address: Ask important contacts for an additional address at a different provider.
  • Get the basics right: rDNS, SPF, DKIM and DMARC help with other providers but do not replace a delisting at Microsoft. See My IP address is on a block list.