Hello Frederic. I hope I'm not late to this.
You don't specify what e-mail software you were using, and what Operating System (WindowsXP, etc) you're using. But lets assume you're on Windows Me or latter and you were using Microsoft Outlook (not Outlook Express). Your e-mails and address book are saved on a file of type PST. Most of the time it's called Outlook.pst. I would recommend that you perform a search on your PC
, and in the search for box type the same thing I typed here: *.PST - and then hit Enter. That is STAR, DOT and PST (*.PST). It will try to locate in your Hard Drive any PST file you can have. You may even have Archive.pst files on your PC
Check on the dates and on the filesize of your PST findings and remember the location. You can even move it to a location easier to access for you if you want. Then open Outlook and from the File menu choose OPEN OUTLOOK DATA FILE and locate that PST file of your seach. You will see it in your Outlook Folder list as usual.
There are more things to it, that will enhance your Outlook usage when these things happen, but its useless to explain here since I'm not sure that Outlook is your e-mail client. I also hope that you're not inside an Exchange network.
Hope this helps!