CleanMyMac 3’s Mail Attachments sorts all the little extras downloaded via Mail by file type — and then helps you clean them out. It removes gigabytes of junk that Mail has stored locally. And, in the event that you need to restore a file, you can always just open the email it came in and re-download the file.
These are files that are stored in the email itself, like zip files, PDFs, signatures, company logos, and anything else someone sends you. For example, if you’ve received emails from Facebook, you’ve probably got multiple copies of the Facebook logo saved to your hard disk.
All the files you open directly from Mail are stored in the Mail Downloads folder. CleanMyMac 3 cleans these locally stored copies out. But again, don’t worry — they can still be accessed in the email from whence they came.