We have a problem where users can't send mail via the Web interface, but they can send mail via a desktop mail client. It was working yesterday and today it's not.

Trying to send via Web interface results in an error of some sort. Here's the error message:

msg - system failure: MessagingException
code - service.FAILURE
method - ZmCsfeCommand.prototype.invoke
detail - soap:Receiver

Anybody know why this is happening?