question about php mail function

Question

什么是smtp，smtp_port？如何获取？

Answer 1

If you have a Windows server, you need to specify the address (domain name och IP) to an sending e-mail server. On real operating systems PHP will always use your local Mail Transer Agent (MTA).

This is clearly explained in the PHP manual: http://php.net/manual/en/mail.configuration.php#ini.smtp

Also, this question is better asked on Serverfault.com