How to send mail if port 25 is blocked

How to send mail if port 25 is blocked

I am trying to send mail from a server where port 25 is blocked. Is there
any free way to send mail.
Here is the relevant PHP code
$subject = "Hello, ".$username;
$message = $username.", you have just become a member of mysite.com. Your
password is ".$password;
$from = "myemail@gmail.com";
$headers = "From:" . $from;
mail($email,$subject,$message,$headers);
The message is accepted for delivery, accoring to my mail log, but it does
not show up in my email.
Again, I just want to send mail without paying for it.