Policies - Attachment Set - Frequently Asked Questions

This article will address the Frequently Asked Questions about the Attachment Sets in the Mimecast system.
 

Q:

Why are files with their file extensions changed from .EXE to .PDF being allowlisted?

A:

If the mimetype is set to "all" for an extension, the policy's checks are: mimetype + mimetype extension "All" + mimetype extension "All" + actual file extension If you have .PDF files with the mime type "all" allowed, and a .EXE file attachment is received that has been renamed with a .PDF extension, the checks will be: application/x-ms-dos-executable + exe = no match in the attachment set All + exe = no match in the attachment set All + pdf = a positive match As a result, the attachment is allowlisted. We recommend careful consideration when creating policies set to allow the mimetype of "all".

Q:	How can I whitelist file extensions that are not listed on my Mimecast Default list?
A:	The team of engineers at Mimecast will assist you if you have a list of file extensions you would like to add or whitelist. Simply add the list to an excel spreadsheet and log a support case with the sheet attached.

Q:	Is there a way to bypass the Mimecast Default blocked list without creating a bypass for all the blocked listed extensions?
A:	Yes, In Mimecast, you can bypass the default blocked list by setting up a separate policy that allows the file type and scopes it according to your email workflow/preferences.

Q:	When configuring the Attachment Set, does this by default block all attachment?
A:	No, this policy specifically addresses the file types or file extension of the attachment. Which means it will trigger if the attachment file is listed in the blocked list.