Question : recipient address rejected relay access denied

All of a sudden, one of my clients box stops sending email.  It receives email fine but does not send it.  Another workstation in the same domain sends and recieves fine.  The error message reads
There was a SMTP communications problem with the recipients email server. Please contact your system administrator
m>:recipient address rejected relay access denied

The server is exchange
Client is Outlook
Domain is Win2k
Network configuration is Incoming DSL split into two networks.

Web browsing is fine.

Please reply ASAP.

Answer : recipient address rejected relay access denied

it's trying to send mail from one SMTP address, by going thru the Exchange server, but that address is not part of the Exchange server's SMTP domain, would be another guess. If your user has a POP account and an Exchange account in the same Outlook profile, he could be responding to an email sent to his POP account, and when the user replies, it tries to go back as his POP email address, not the Exchange address.The exchange server rejects it. It's an odd situation I used to deal with, but not frequently.