Sending email with PHP from an SMTP server

Question

I get an error: SMTP server response: 530 SMTP authentication is required. when I tried to send an email in PHP

mail function]
; For Win32 only.
; http://php.net/smtp
SMTP = localhost
; http://php.net/smtp-port
smtp_port = 25

; For Win32 only.
; http://php.net/sendmail-from
sendmail_from = someonelse@example.com

This is the setup in the php.ini file. How should I set up SMTP?