I am having problems getting the system to download larger emails (20 mb and over - but this is variable). Initially the log complained that messages were over the maximum default 10 mb size. I altered the settings in Exchange Management Console:
Organisation, Hub Transport, Global Settings, Transport Settings - max send/receive set to 50720
Organisation, Hub Transport, Send Connectors, Windows SBS Internet Send - max. message size box unticked
Server, Hub Transport, Receive Connectors - all 3 receive connectors set max. message size to 17480 - too small I know - but it was set larger and I got the error below.
This did in fact allow the connector to download emails up to the 17480 limit. BUT if I set these limits up higher (say 50720), the POP3 connector would fail to download the large emails (15-20mb - so well below this limit) with this error:
Cannot connect to the SMTP server 'localhost' on port 25. The error code was 0x800ccc0f. Verify that the Exchange Transport service is running and that the Exchange Receive connectors are properly configured.
This error would only occur if there was a large email in the POP3 box - if there were no large emails then there would not be any errors.
By dropping the Receive connector sizes down to marginally above the size of the email to be collected - it would eventually collect it. By the way, I can Telnet to Localhost on Port 25 no problem.