Hi,
Exchange has a default limit of 10MB on the Receive Connector, which is independent of the limits set under "Global Settings - Message Delivery" and affects the delivery through SMTP from PopGrabber.
To increase this limit please execute the following command:
Set-ReceiveConnector -identity "Default [SERVERNAME]" -maxmessagesize 30MB
You can of course change 30MB to whatever your ISP uses as limit (20MB to 30MB is the most common).
If this does not work, you may have limits set on the Transport Server.
Please check this article for complete information on Exchange 2007 Message Size Limits:
http://technet.microsoft.com/en-us/library/bb124345%28EXCHG.80%29.aspxRegards,
Eclarsys Support