When email is being protected by an external cloud based solution the default connectiontimeout interval for exchange 07/10 is 10 minutes. And normally this is not enough for eg. Forefront Online , Postini, Messagelabs.
So here is some powershell commands to resolve the issue.
Firstly Get-ReceiveConnector | fl Id*,*connectiontime*
Change the ConnectionTimeOut value
Set-Receiveconnector -ConnectionTimeOut 00:20:00
Name of connector is specified by ServerName\receive connector name