Display Unread E-Mail Count on Loginwindow
I think @Buscar웃 is right, you need to fetch your mail before you know how much mail is in your inbox.

I think you can use your Terminal for that, and with the combination of 'GeekBench' it might even look pretty.

A common mailclient for OS X terminal is mail, it is already installed, but unfortunately I have no clue on how to configure it correctly.

Another terminal mail client is mutt. You can install mutt using brew

brew install mutt


You can then configure mutt and run it in your other account. Mutt is lightweight and will not use much resources.