Part of our EU mail infrastructure was blocked by Hotmail. The affected servers were:
- smtp2.de.opalstack.com (outgoing mail)
- mx1.de.opalstack.com (incoming mail and forwarding)
We've already dealt with the issue and Microsoft have confirmed that the servers have been unblocked, but it may take a few more hours to take full effect.
We'll update this post when we've confirmed that mail is no longer being blocked.