Unless I miss my bet, I think they're gone. If you have a backup like Time Machine though, they can be recovered. But if you don't, you might consider buying an external and start backing up so you won't have another loss like this one.
Your kidding right? How can they delete all your e-mails without giving you a warning? I hit the minus button when the wrong account was highlighted and poof gone without any warning or any are you sure pop ups... There has to be a way to bring them back.
Are you using Mac Mail? I don't use it, but notice there isn't a minus button in Mail. But, go to Mail Preferences and check the Mailbox Behaviors. What did you check there in "Trash?" Your deleted messages may be on the server in the mailbox trash...
You could also go to Mail Help and put in "deleted" and there should be an item on recovering deleted messages...
my colleague has just accidentally deleted a mailbox through apple mail. is there any way we can restore it?? it contained rather a lot of project emails and we will be a bit stuffed if it has gone completely!