Background:
Exchange 2007 complains that your outbound and inbound emails are too large. As you send them, you're told that you should "make the message smaller" by "removing attachments". By default, the limit is set at 10 MB.
#550 5.3.4 ROUTING.SizeLimit; message size exceeds fixed maximum size for route ##
Solution:Fire up the Exchange console and get a listing of your connectors with their current size limits:get-receiveconnector | select identity,maxmessagesize
Then change the limit:set-receiveconnector "Connector Name" -maxmessagesize 30MB
All Edge-Sync Servers will need to download their configuration again from the DCs. Run this on all EdgeSync bridgeheads:start-edgesynchronization
Update:
As mentioned, you may also have issues with the transport limit.
get-transportconfig | fl *
If the limit is set to "unlimited", you will need to explicitly put a limit in:set-transportconfig -MaxRecieveSize 30MB
More information:
http://technet.microsoft.com/en-us/library/bb310771.aspx