Why are attachments not being dropped by name filter on ESA?

Question:

Attachments not being dropped as expected and one of the following:

Message Filter using drop-attachments-by-name
Content Filter using Drop_Attachments_By_Name_Action.

The Drop Attachments by Name action finds the files name in one of two ways.  First it checks the filename as declared on the MIME header data.  The second method only happens with archives: the files in the archive are extracted so the filenames can be listed.  If the attachment is an archive and the extracted content's total size is greater than the max scan size or exceeds the max scan depth, the filenames will not be obtained.

There also may have been a scan error on the message and it is possible that the detected MIME type is configured to be skipped.  To find out the exact cause for a given message, search the mail logs using grep from the CLI.  When you search on the MID, any scan issues will be reported on their own line.  Here is an example:

Tue Aug 3 16:36:29 2004 Warning: MID 256, Message Scanning
 Problem: Continuation line seen before first header