trying to use Gmail SMTP servers for vB emails, but it's not working

[Fangs404]

I'd like to use Gmail's SMTP server to send all forum emails because we've been having some issues sending emails. A lot of free servers will accept them from our server (like Gmail and Yahoo!), but most school and business email addresses never get the email confirmation sent to them. I figure that using Gmail's SMTP server will fix this, but it's just not working. Here're the settings we're using:

SMTP server: smtp.gmail.com
port: 465
SMTP username: [username]@gmail.com
password: [password]
SMTP secure connection: TLS

When running the diagnostic, there's a delay of about 30 seconds, and then we get this error:

Pertinent SMTP Settings
SMTP: tls://smtp.gmail.com:465
SMTP Username: [username]@gmail.com

The mailing function returned an error while trying to send the mail.
The following errors were outputted by PHP when attempting to send mail:

Warning: 0 Unexpected response when connecting to SMTP server in [path]/includes/class_mail.php on line 601

Does anyone have any idea why this is happening?

[edit]
This might better belong in Forum and Server Management. Oops.