Since occasionally conversation bubbles up on new SBS clients who use POP and transition to SMTP you likely will on occasion see errors in the monitoring reports related to the POP Connector. This article expounds on this subject.
One interesting point I discovered while reading this today is that CDO (Collaborative Data Objects) is used to retrieve and transfer the POP mail to the SMTP side of Exchange. CDO is also mentioned in BlackBerry documentation for the current 4.1.6 upgrade under the directions of Windows patches recommended to be installed in preparation.
POP3 Connector overview
When you use the POP3 Connector to retrieve e-mail, the following mail-flow process occurs:
The Connector for POP3 Mailboxes service connects to and logs on to the remote POP3 server.
The Connector for POP3 Mailboxes service downloads e-mail messages and stores them in the following folder:
%PROGRAMFILES%\Microsoft Windows Small Business Server\\Networking\POP3\Incoming Mail
When all the e-mail has been downloaded from the remote POP3 server, Collaborative Data Objects (CDO) on the Windows Small Business Server-based computer retrieves the e-mail messages from the Incoming Mail folder. The headers of these e-mail messages are modified to indicate that the e-mail messages will be directed to a local Exchange mailbox, and then the e-mail messages are saved to the following folder:
If CDO cannot move an e-mail message to the PickUp folder, the e-mail message is put in the following folder instead:
%PROGRAMFILES%\Microsoft Windows Small Business Server\\Networking\POP3\Failed Mail
If an e-mail message is corrupted, it may not be moved to the Failed Mail folder. In this scenario, the corrupted e-mail message remains in the Incoming Mail folder.
All the e-mail messages that are in the PickUp folder are processed by the local SMTP service and are delivered to the appropriate recipient.
When you use the POP3 Connector to retrieve e-mail messages, those e-mail messages are not processed by any of the following Microsoft Exchange Server 2003 components:
The Intelligent Message Filter add-in
Because the POP3 Connector uses CDO to transfer e-mail messages to the SMTP PickUp folder, these e-mail messages bypass the filtering mechanisms that Exchange 2003 contains.