New mail arrival announcement

Hi Guys,

I am new to Linux and I am running Slackware.. Kernal 2.0.30.  Whenever a
new mail arrives for a user, there is a message which flashes up on all
sessions of the user.  

This is irritating and at most times undesirable, as it prints half the
mail alongwith the message.  How do I turn this off?

I am sure one of you guys can help
:)

j0se