Even with the Disarm feature in Symantec Messaging Gateway (SMG) enabled and MHTML files passing through the SMG without being disarmed.
Currently the Disarm feature is not designed to scan MHTML files.
In its current implementation, the Disarm feature does not scan MHTML files.
To block MHTML files, create an Attachment List for MHTML files and then associate that Attachment List with a Content Rule
To create an Attachment List for MHTML files
To Create a content rule to block MHTML files