I am using Ubuntu 10.04 and by following this tutorial I have made RT run well in everything except for sending outbound emails. The difference is, I need to make RT use an external, existing mail server. The mail server is accessible via SMTP with authentication so I am looking for a place to insert the username and password, but nothing like that seems to exist.
The closest thing that I found by googling is that I need to setup ssmtp or msmtp and use it to forward my outbound emails to the mail server (sorry I lost the link). Is that true? Are there any (perhaps better) other ways?
Getting RT to use an external SMTP server is easy, except for the authentication part. As you have surmised, to use authenticated SMTP you need the support of another program, either a properly configued system MTA like Postfix or Sendmail or a minimal MTA like msmtp. This question has been asked (and answered) frequently on the RT mailing lists:
Install one of them:
It will create a symlink from sendmail to msmtp, which will forward to any SMTP server you configure. Then configure RT to use sendmail.