In the old days...

[GuiltyPleasure]

...there used to be an option that allowed you to check back on sent PMs, it seems to have gone. Any takers?

 

[Yardley]

On these kind of forums you can "request a read receipt" when you send a PM.

I never saw the point. If the person doesn't reply, what difference does it make when they read it?

 

[RejectReality]

When you send a PM, there's a box at the bottom that is checked by default for "keep a copy in the sent folder".

If you haven't been unchecking that box on your PMs, then you can go to your private message page, and directly below the indicator of how much storage space you're using, you'll find a drop-down. Use it to switch between your sent and received folders.