Increase MaxHeaderSize on Exchange 2007 and Exchange 2010
Emails with large headers/many recipients bounce to external senders with 4.4.7 Could not deliver the message in the time limit specified.
To check current configuration:
Get-ReceiveConnector | ft name, MaxHeaderSize
To set a new limit:
Set-ReceiveConnector “Windows SBS Internet Receive Servername” –MaxHeaderSize 128KB