Exchange 2013 SP1 (CU4) patch issued
Microsoft has issued a patch to address formatting issues that could cause problems with third party Transport Agents. Check it out here:
Here’s the explanation that shows up on the CU4 download page.
Since the release of Microsoft Exchange Server 2013 Service Pack 1 (SP1), Microsoft has become aware of an issue that affects some customers who use transport agents that are provided by third-party OEMs. For more information about this issue and a supported fix, see the following Microsoft Knowledge base article:
Third party transport agents cannot be loaded correctly in Exchange Server 2013