Ok, I understand better now.
I am not using KDE4, and not sure where it keeps "Trash" but it might be
so you could try
To see the hidden files in Trash
Kmail may be very different in KDE4.
In my /home/tred/.kde/share/apps/kmail/mail/inbox
directory I have three further directories cur tmp
Read mail is kept in the new
directory and mail messages have names like
Please don't do any more reboots until you are sure your email is not recoverable (although it might be too late, now that you have already rebooted).
Perhaps it would be wise to copy all of trash to somewhere "safer" like /home/kapten/LostStuff
before some "tidying up" process comes along and empties your "trash". Then you can reboot as much as you like.