That's pretty much it: are there any tools to recover my e-mails from Outlook for Mac 2011?
Mine crashed and the auto-correct only recovered a few weeks worth of e-mails, everything else was gone no matter what I tried. They're also gone from the server as I ste Outlook to delete them once they were downloaded.
Any ideas..?

By auto correct you meant rebuild the database?

To rebuild the database hold down the option key while launching Outlook.

You can also replace the database from a backup, which I hope you have. Something like Time Machine.

Yep, I meant rebuild the database, sorry. It doesn't rebuilt in full, only a few weeks worth.
And I did had a backup on Dropbox, but it got corrupted when I tried to download it...

Dropbox and MS mail databases don't mix as you've found out. Outlook waits until you close the program to write changes to the database. The problem is the database is one file with everything inside it. The database can get quite large so the sync can take a while. If it's stopped in mid sync to DropBox it can get corrupt.

It is recommended that if you do back it up to DB you make sure that you first quit Outlook, then give DB a chance to sync. It's best to not trust it as you've seen.

DropBox also has a feature, if you go on their website to your account, they have previous versions of all of your stuff for the last 30 days so you may have a chance that a good one got backed up recently.

I don't know what else to do, sorry.