I'm new around here ... and hope it's okay to pass along a little idea I just came up with.
I recently cleaned out (mostly by several hours of replying with some ruthless deleting, etc.) my Apple Mail INBOX and Sent Folder. Years worth of stuff. Out-of-control. Usually when the program loads, it takes a second for all the mail to appear. This is not a defect, per se, but the way the program seems to work. In the past it was a little disorienting to see an INBOX with no mail in it ... until the split-second or two when it all loaded and I could sigh a little with relief.
Now when I open up Apple Mail, the INBOX is blank and stays blank ... for a great reason! So I sent myself an e-mail with the subject line "BELOW THIS SHOULD BE YOUR EMPTY MAILBOX!" and it resides there permanently. So now when my INBOX opens up "empty" I know the program is working correctly AND I'm feeling pretty good about why it looks that way!