PHP mail suddenly stops sending messages

Hey all…i’m a bit baffled by this one.

First off I have 4 intranet forms that our company’s users can go fill out for requesting various information form the I.T. dept. (i.e. New user form, leave/vacation form, Employee of the month form, etc)

I have made no major changes to the php code nor ANY changes to the server itself (it is a Red Hat linux box running apache, i can get specific versions if it makes a difference). Suddenly my mail functions are not working (they have worked previously and flawlessly)

Is there anything on the server that i might check? THanks For the help in advance!