Before I type anything else, allow me to state that running a search and deleting things with a script from a users (or a loop of all users) is a very dangerous process. However, I’ve often noticed that an outbreak of bad things can cause us to do some pretty awesome things. So, you can use the get-Mailbox cmdlet to pipe a mailbox into the search-mailbox cmdlet and from there use the -SearchQuery option to search for an attachment, following the attachment option with a filename and then delete it using the -DeleteContent option. The example would be as follows:
You can also filter search queries based on To, From, CC, Subject, Sent date and of course, policy data. You can also use the -TargetMailbox and -TargetFolder options to move messages into a quarantine mailbox/space.