From what we can see in the log file, PopGrabber is delivering the messages to the SMTP server but at this point the SMTP server is probably forwarding it to another server (or sending a Non-Delivery Report back) instead of delivering it locally.
If you are using Exchange 2003 please enable message tracking as explained in this article:
http://www.msexchange.org/tutorials/Exchange-2003-Message-Tracking-Logging.htmlYou can then check what the Exchange server is doing with the messages received from PopGrabber.
For exchange 2007 please check the following article:
http://www.msexchange.org/tutorials/Exchange-2007-Message-Tracking-Part1.htmlAnother thing to check is that Exchange is configured as authoritative server for the ########.org domain, as described in this article:
http://support.microsoft.com/kb/823158Let us know if this helps.
Regards,
Eclarsys Support