One of the users here at work has been emailing with a gentlemen for the past week, then all of a sudden, yesterday, she couldn't email him anymore.

This is what we get for a NDR.

Code:
There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.

            <mail.XXXX.com #5.5.0 smtp;550 <xx-xxx-xxx-31.static.twtelecom.net[XX.XXX.XXX.31]>: Client host rejected: REJECTED S25R RULE>
This is the SMTP log

Code:
208.XXX.XXX.7, OutboundConnectionCommand, 6/26/2007, 10:04:48, SMTPSVC1, UAM-DC, -, 281, 0, 4, 0, 0, RCPT, -, TO:<[email protected]>,
208.XXX.XXX.7, OutboundConnectionResponse, 6/26/2007, 10:04:48, SMTPSVC1, UAM-DC, -, 422, 0, 101, 0, 0, -, -, 450 <XX-XXX-XXX-31.static.twtelecom.net[XX.XXX.XXX.31]>: Client host rejected: 450 REJECTED S25R RULE,
208.XXX.XXX.7, OutboundConnectionCommand, 6/26/2007, 10:04:48, SMTPSVC1, UAM-DC, -, 422, 0, 4, 0, 0, RSET, -, -,
208.XXX.XXX.7, OutboundConnectionResponse, 6/26/2007, 10:04:48, SMTPSVC1, UAM-DC, -, 484, 0, 6, 0, 0, -, -, 250 Ok,
Not really that sure where to go from here with it....this is Exchange server 2003, and it does have the GFI mail essentials package on it.

I googled that S25R rule, but have not been able to find much on it other than some sort of Anti-spam tool maybe?

Any help would be appreciated..thanks