I upgraded Redhat 7.3 - 9 and now PHP will not send email. PLEASE HELP!

[Eric]

I upgraded my server from Redhat 7.3 to Redhat 9. Now all my programs
that send email through PHP do not work. Do I need to set something
else somewhere? I have Redhat 9, Apache 2.0.40 and PHP 4.2.2