Php ini_set mail smtp

How and where to insert script for php ini_set mail smtp i create wiki for my site but whan some one register it need to receive mail to confirm registration but whan some one try to register he get this message:

开发者_如何转开发wiki could not send your confirmation mail. Please check your e-mail address for invalid characters. 

Mailer returned: Failed to connect to mailserver at "localhost" port 25, verify your "SMTP" and "smtp_port" setting in php.ini or use ini_set()

so i will not edit php.ini i need script for ini_set() pls help

Your mail server might not be running. Contact your system administrator and ask to check if the mail server is running on 127.0.0.1:25