PROBLEM:
Emails with attachments are not delivered to exchange 2010, or 2007 server.
SOLUTION:
The problem is possible due to the time out setting on the receive connector in exchange.
Use the Set-ReceiveConnector cmdlet to change an existing Receive connector.
EXAMPLE:
This example makes the following configuration changes to the Receive connector Internet Receive Connector:
1.) Sets the Banner to 220 mail.example.com OK.
2.) Configures the Receive connector to time out connections after 15 minutes.
Set-ReceiveConnector -Identity "Internet Receive Connector" -Banner "220 mail.example.com OK" -ConnectionTimeout 00:15:00
REFERENCES:
http://technet.microsoft.com/en-us/library/bb125140.aspx
http://technet.microsoft.com/en-us/library/bb124740(v=exchg.150).aspx