When Microsoft (MS) Exchange 2007 is the Mail Transfer Agent (MTA), you cannot send emails with attachments larger than 10 MB. Instead, you receive a Non-Delivery Receipt (NDR) with the error:
(0x80040610): The message being sent exceeds the message size established for this user.
However, there are no policies set to block attachments larger than 10 MB in the HES/HES - Inbound Filtering console.
MS Exchange Server 2007 sets 10 MB as the default global message limit. This is Microsoft's best practice to help prevent Denial of Service (DoS) attacks.
To adjust this limit to the desired attachment size, check the information on this Microsoft KB Article: Modify Exchange 2003 Global Message Size Limits in Exchange 2007 RTM.
In case making changes to the message size limits is not possible due to permissions or restrictions, contact your MS Exchange Administrator. Alternatively, you can contact Microsoft Technical Support for assistance.