Well, you'll be using an SMTP server when sending mail, and you can set it in two ways (okay so there's more, but here's what you want to know):
- Alter the php.ini file (this would be if you own/are the admin of the server, obviously) - more specifically, this section:
[mail function]
; For Win32 only.
SMTP = mail.example.com
; For Win32 only.
sendmail_from = myAddress@example.com
; For Unix only. You may supply arguments as well (default: "sendmail -t -i").
;sendmail_path =
OR
- Set it on-the-fly in your PHP script using [man]ini_set/man. Just set the SMTP directive to the SMTP server you send mail through.