"You have mail." notification in shell - how to get rid of it?

Question

Hey guys,
whenever I start a shell (zsh, but same for bash/csh/ksh) I get the message that "You have mail.". Well, that's true, there are mails in my /var/mail/`whoami`. But as they ain't new, I don't need, and more, don't want this message. How do I turn it off?
It's gone when I move my mail from /var/mail/$USER to somewhere else, but that is no solution.
Ideas? Clues? ANYthing?

Answer 1

There's something strange in how Terminal.app invokes
the shell that I haven't had time to trace down yet;
I can see the following:
Terminal.app with default settings does not invoke
~/.bashrc but displays the "you have mail" message.
Terminal.app set to launch /bin/bash neither invokes
~/.bashrc nor displays the "you have mail" message.
xterm in X11 invokes ~/.bashrc and does not display
"you have mail".
I always use xterms because they seem to have better
compatibility with more shell commands than
Terminal.app.
The one thing I didn't try is to put the the
MAILCHECK=-1 in /etc/profile and then reboot.
Well, I use iTerm, but it's the same for Terminal.app
I also tried MAILCHECK='', MAILCHECK='-1' and all that... and if I check it, it's set, but still this **** message...
Geez, it can't be thaat hard, I thought!?