Installing PHP to find SMTP server ...

Hi: Newbie here. I'm getting ready to do a custom install of PHP on a Pair Networks FreeBSD server. I've never done a Unix/Linux install before, so I'm confused about something. How do we tell PHP which SMTP server to use? For Windows systems, it tells you to put an entry in the php.ini file. But for Unix/Linux systems, it doesn't mention anything. How do we install PHP on a FreeBSD server so that the mail( ) function will work properly? I haven't attempted the install yet, but this seems ahead of time to be a potential problem. Am I missing something? Does PHP already know how to find the SMTP server? Thanks in advance.