Been running version 5 for a few months now. Today, noticed this error when attempting to send new emails:

A network service error has occurred. msg: system failure: MessagingException
code: service.FAILURE
method: SendMsgRequest
detail: soap:Receiver

And, the emails aren't sent.

The network is up. smtp ports are open. All the services appear to be running. Don't have a clue as to where to look. Any suggestions?