Question : POSTFIX - Configuring SMTP authentication for outgoing email

We use Nagios for network monitoring and it works great except for sending out emails to our email server.  The issue is that our email SMTP server (hosted by another company) requires SMTP authentication.  I was able to setup an SMTP relay on a Windows box and set postfix to relay mail to this box.  The delima is if the windows box goes down or if the relay service stops then I won't receive any of the Nagios email notifications.  What I would like to be able to do is configure postfix to send the mail directly to the SMTP server and provide the necessary  authentication.  How can I do this?  Do I need to modify postfix?  I don't see a way to add authentication information in Nagios and I don't think that there is from what I can tell by the Nagios documentation.

The Linux OS is Cento5.  Postfix, send mail, procmail and Cyrus were all installed by the default install.  I assume that postfix is configured with cyrus in mind but I don't know.

Answer : POSTFIX - Configuring SMTP authentication for outgoing email

This might be the solution you're looking for then. I don't know if the relay host portion will work against POP or IMAP logins.

Setup Relay Host Port and SMTP Authentication Client in Postfix
http://wingloon.com/2008/06/21/setup-relay-host-port-and-smtp-authentication-client-in-postfix/

Enabling SASL authentication in the Postfix SMTP client
http://www.postfix.org/SASL_README.html#client_sasl