We have two Ms Exchange Servers both 2003 and configured as: FE (front end) and Back End (for meilboxes) - currently the FE is published through Ms ISA 2006 and working just fine.
Plans to migrate to TMG 2010 publishing of the FE named above have hit a snag by some very strange issue of -- inbound emails with attachments above 1MB just never get delivered -- kindly note that there's zero limits put currently.
However outbound emails with 1MB and above etc are delivered into the internet.
TMG 2010 has not been configured to do any email security of any kind and yet we are facing the above issue.
We are able to do tests by simply changing the gateway for the Exchange FE to either ISA box or TMG -- it's just so disturbing.
Software/Hardware used: Ms Exchange 2003, ISA 2006 and TMG 2010 and windows 2003 and 2008 with respective latest service packs