Outlook filters for >x people in CC possible?

Hi all,

I've got a bit of a spam issue that isn't solved by either keyword or actual spam filter. The problem is that I'm in China and mass email marketing here is acceptable for some reason, so local spam filters don't catch the perps, and international ones are useless based on the language.

And since I'm in a customer/supplier facing role, quite a few genuine mails use the same keywords as the spammers, so that doesn't work to fix my problem.

However, the mails are usually sent to hundreds of people at once, all with their mail addresses in plain view in CC.

So I'd just like to set up a filter to send mails with >100 recipients or something like that straight to trash, but can't seem to find it in the outlook rule settings.

Does anyone know of a useful workaround?

Thanks!