Summary
You want to know if it is possible to receive attachments bigger than 50MB in HES.
Details
No, it is not possible. This is the second rule of the HES - Inbound Filtering policies, and it cannot be changed in the HES - Inbound Filtering version.
This rule is designed to protect the system from Denial of Service (DOS) and Zip of Death attacks. If the size of the incoming message exceeds the default limit of 50MB, or if it has been sent to more than 50 recipients in the organization, then the message will be deleted.
Only HES customers may modify this rule up to the system limits of 50MB and 100 recipients.