Can I create an exception for scanning emails?

Hello

We've recently changed our website and so we'll be starting to get emails from the website as Encrypted PDFs.  The first couple that I've gotten have "Warning: Antivirus Unscannable (Encrypted)" in the Subject heading before the Subject itself

So I don't have to remove that every time I reply to one of these emails (cause I know I'll forget) is there some way I can stop those particular files from being scanned?

They won't be the same PDF name each time, or from the same address each time but they will have the same Subject heading each time so can I protect that heading from being scanned?

Any help gratefully appreciated!

Cheers.

Melissa.