We are currently experiencing problems with our SMTP Mail server. Some users may experience problems authenticating and sending emails through the server. We are investigating the issue and will update when we have more information.
2016-08-23 15:05 UTC: The SMTP authentication database was corrupt, so we’ve restored it from a backup made on 18 August 2016. Most mailboxes should be able to send mail now. If you’re still having problems, then please try resetting your mailbox password via our control panel.