If you are having problems connecting or sending emails through your SMTP server, please note:

1. The new rewrite of class.smtp.php provides more information about the processing/errors taking place
2. Use the debug functionality of class.smtp.php. To do that, in your own script add the debug level you wish to use. An example of that is:

$mail->SMTPDebug = 1;
$mail->IsSMTP();
$mail->SMTPAuth   = true;
$mail->Port       = 26;
$mail->Host       = "mail.yourhost.com";
$mail->Username   = "name@yourhost.com";
$mail->Password   = "your password";

Notes on this:
$mail->SMTPDebug = 0; ... will disable debugging (you can also leave this out completely, 0 is the default
$mail->SMTPDebug = 1; ... will echo errors and messages
$mail->SMTPDebug = 2; ... will echo messages only
... and finally, the options are 0, 1, and 2 ... any number greater than 2 will be interpreted as 2

And finally, don't forget to disable debugging before going into production.

Enjoy!
Andy