Yes, PHP mail() function can be used to send out mail. PHP mail() function is supported on Linux plans only. The mail() function is not supported on our Windows plans due to the fact that there is no accounting procedure for the emails sent using php sites. Therefore, to make sure abusive accounts are not able to freely send spam emails from our Windows servers, we have disabled the mail() function.
To send mail through PHP on Windows, you can use the Net_SMTP pair package. The documentation is available at: http://pear.php.net/reference/Net_SMTP-1.1.2/li_Net_SMTP.html
Otherwise, we strongly suggest using a linux plan if you plan on deploying applications that require to send mail on php.