CAUSE
This problem can occur because Microsoft Exchange Connector for POP3 Mailboxes has the POP3 server's IP address listed as the "POP3 Mail Server" for the Exchange recipients on the Users Mailboxes tab, in the POP3 Connector properties.RESOLUTION
To resolve this problem:
Click Start , point to Programs , and then click Microsoft Exchange/Microsoft Exchange Administrator .
Double-click Connector for POP3 Mailboxes .
In Connector Properties , look for entries that have IP addresses listed for the POP3 mail server on the Connect & Download tab in the Global ISP Mail Hosts dialog box.
Look for entries that have IP addresses listed for the POP3 mail server on the User Mailboxes tab for any listed recipient.
Change all POP3 mail server IP addresses to their fully qualified domain names (FQDN) by using the Edit button on the appropriate tab.
Click OK , and then click Services in Control Panel to stop and start Microsoft Exchange Connector for POP3 Mailboxes.
This is from document ID:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;Q242210
Hope this helps.
Humbly submitted,
diabetic