Mail 1.3.11 Deleting Emails

[lannette]

I'm using Mail 1.3.11, on my Mac (10.3.2). I opened it up today, and quite a few emails I had received yesterday were missing. They were in my inbox - I didn't delete them. I double checked my trash and junk folders, just to make sure, but the emails are gone...

Is there any way to retrieve them? And a way to prevent this from happening again?

Thanks!