We've moved a few services around to reduce the load on our main server. This has meant shutting down some services on IPs where they had been for years. In particular if you used:
* smtp to 18.104.22.168 or 22.214.171.124 (old DNS for old mail names)
* any service on 126.96.36.199-62 (had been out of DNS for a while, but old mail.messagingengine.com and www.fastmail.fm)
* authenticated SMTP through any server other than mail.messagingengine.com
Then you may have noticed that the service went away in the past 24 hours. The main reason for removing these services was that the machine hosting them is also used for outbound email, and by allowing SMTP there a particularly clever spammer managed to bypass our rate controls for one spamming run (we noticed the increased load in the daily report that evening and shut down the technique they had used).
For the vast majority of users: nothing has changed. For the few who were doing something tricky, you can use the IP address 188.8.131.52-162 in place of .60-.62 if you need to. If you have put explicit IP addresses rather than CNAMEs in your DNS and you're not hosting with us, then tough - you're doing something naughty and things break when you do that - fix the entries!
To discuss this, head over to this forum thread.