Security researchers will be publishing what they claim are critical vulnerabilities in PGP/GPG and S/MIME email encryption on May 15. In the meantime, EFF advises you disable PGP email clients. GPUPG offers different advice.
If you're running low on disk space on your Mac, especially SSD space, every extra bit can count. One of the places you can often scrape out a few extra megabytes or even gigabytes is Mail Downloads. Any attachments you open in Mail or Quick Look gets saved right to that folder. Chances are you don't need them, especially the old ones, and trashing them will free up some valuable space.
If you use the default Mail app on your Mac and you're running OS X Mountain Lion, you can add a sender to your VIP list just as easily as you can on your iPhone or iPad. VIP list basically will filter out emails you want based on who is sending them, therefore making finding messages a lot easier. Don't know how to use VIP Inbox on your Mac? Here's how: