I migrated an application to a platform without a local transport agent (MTA). I did not want to configure an MTA, so I wrote this xxmail function to replace mail() with calls to a remote SMTP server. Hopefully it is of some use.

function xxmail($to, $subject, $body, $headers)
{
 $smtp = stream_socket_client('tcp://smtp.yourmail.com:25', $eno, $estr, 30);

 $B = 8192;
 $c = "\r\n";
 $s = 'myapp@someserver.com';

 fwrite($smtp, 'helo ' . $_ENV['HOSTNAME'] . $c);
  $junk = fgets($smtp, $B);

 // Envelope
 fwrite($smtp, 'mail from: ' . $s . $c);
  $junk = fgets($smtp, $B);
 fwrite($smtp, 'rcpt to: ' . $to . $c);
  $junk = fgets($smtp, $B);
 fwrite($smtp, 'data' . $c);
  $junk = fgets($smtp, $B);

 // Header 
 fwrite($smtp, 'To: ' . $to . $c); 
 if(strlen($subject)) fwrite($smtp, 'Subject: ' . $subject . $c); 
 if(strlen($headers)) fwrite($smtp, $headers); // Must be \r\n (delimited)
 fwrite($smtp, $headers . $c); 

 // Body
 if(strlen($body)) fwrite($smtp, $body . $c); 
 fwrite($smtp, $c . '.' . $c);
  $junk = fgets($smtp, $B);

 // Close
 fwrite($smtp, 'quit' . $c);
  $junk = fgets($smtp, $B);
 fclose($smtp);
}