Hey no problem with this... quite simple.
I need you to open up the php.ini file and hit cntrl+F to search.
Search for [mail function]
Then you will see a line that says :
; For Win32 only.
SMTP = xx.xx.xx.xx (put in your SMTP server)
smtp_port = 25 (that is usually the case)
; for Win32 only.
sendmail_from = mailaddress@address.com (this MUST be a valid E-Mail address that your server knows of)
That sendmail_from address is the address that all mail will go out from. Usually we set it up as donotreply@isp.com. Then disable incoming mail. That way they can send mail out but not have it come in.
Take care and hope this helps.
Chad