Sent mail is missing! Please help!

Just had my sent mail disappear (with the exception of about six emails). At first I thought it was simply a problem in Outlook, but when I logged into my web mail account they weren't there either. There were 3 years of messages on there.

I didn't actually delete anything accidentally - just gone.

Please help, there is a lot of information that I require, it would be devastating to me if I lost this. I hope this is a temporary situation, or it can be restored.

Jason