Please Help on Send failure

[jeff]

Hello
very first time in my life trying to install a webmail.
Unfortunately, I'm experiencing mail send failures.
Receiving mail are ok.
Log reports
[06-Oct-2006 10:23:04 -0600] SMTP Error: SMTP error: Connection failed: Invalid response code received from server
 in /home/mysite/public_html/roundcube/program/steps/mail/sendmail.inc on line 253


I've attached my current main.inc.php file.

Could you PLEASE help me?

Thank you.