Need help

Neomail has been working on this server for 2.5 years now.
All of a sudden today when any user that logs in tries to send an email 
thru neomail this error is received:

Error Sending Mail
Sorry, there was a problem sending your message.
Please click your browser's Back button,
check your message, and try again.

Nothing that I am aware of has changed.
POP3 and Sendmail using email clients still is working 100%, just neomail 
won't send an email.
No errors in the neomail.log, none in the servers maillog.

Anyone have a clue where to look?

Richard





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