What script is used to send mail?

Have installed the ladder software on my internal Debian server, and all works well - except I cannot get the system to send emails.

My server is a little odd as it uses a different server to actually send mail, so I need to specify the IP address and port number of the mail server for things to work. For example, I had to edit some php files for a phpbb2 forum I run to get it to work.

I have looked through the php files for the squash ladder (noting that I am not a PHP expert!) but I cannot find what it actually calls to send email, so i cannot see where I might be able to specify the email server address or port number.

If anyone can point me in the right direction it would be appreciated.