Configuring Nagios to send e-mail through external Postfix server

Is there a set of instructions or a basic 'how-to' for configuring Nagios to send notification e-mails through a external e-mail server that uses Postfix/Dovecot? Our Postfix environment is configured for SSL/TLS encryption, thus we require all external accounts to login before sending e-mail, thus the environment is not just a simple relay.

OS Platform: RHEL 5.5
Nagios Version: 3.2.3
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Michael WorshamInfrastructure / Solutions ArchitectAsked:
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Sanga CollinsConnect With a Mentor Systems AdminCommented:
That should get you going. Sendmail can be called only when nagios needs to send an alert. Configuring it to use the relay only will also allow you to keep an eye on any emails coming from the monitoring server
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Deepak KosarajuDevOps EngineerCommented:
set the relay host inside /etc/postfix/main.cf to the hostname of your mail server in your platform:
relayhost = hostname.$mydomain
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Deepak KosarajuDevOps EngineerCommented:
Oh sorry my bad i should have read the complete question.
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Sanga CollinsSystems AdminCommented:
i believe you would need to setup sendmail or postfix on the nagios server and configure it for authentication based relay.
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Sanga CollinsSystems AdminCommented:
here is the guide i use for postfix smtp authentication relay. It cover TLS which you will need since your main server uses SSL/TLS authentication
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Michael WorshamInfrastructure / Solutions ArchitectAuthor Commented:
@sangamc Due to DISA/STIG requirements, installation of Postfix/sendmail on the originating (monitoring) server isn't allowed. It must use an external e-mail server already configured for SSL/TLS and part of the AD/LDAP and DNS infrastructure.
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Sanga CollinsSystems AdminCommented:
You will need some way to get the email from the nagios server to the external email server. According to nagios documentation you must install some form of mail utility to accomplish this. There is one other way i can think of however. Since the nagios mail command just runs a printf and the sends that result to postfix, you can modify ti to printf to a file in a predetermined directory, and have the external mail server run a script on a 5 minute schedule for example to connect to the nagios server and pull any notifications that may have been saved in that directory and then send them.
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Sanga CollinsSystems AdminCommented:
i am not familiar with the details of DISA/STIG requirements, but wouldnt a workstation configured with outlook connecting to the external server be the exact same thing. all nagios does in a relay scenario is act like a workstation sending outgoing mail. without the external server it will not be sending mail.
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Deepak KosarajuDevOps EngineerCommented:
@sangamc - suggestion make sense but #mwecomputers its worth getting approval to install either postfix r sendmail agents on nagios server secure it tight just to allow the relay traffic to the mail server, this can give u the accuracy on the time of alerts and could save you lot of time.
@sangamc - In your previous post I think you forgot to share the guid to use postfix smtp auth relay procedure.
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Michael WorshamInfrastructure / Solutions ArchitectAuthor Commented:
Well I consulted the powers that be. They would allow postfix or sendmail to be installed, just not actively running (listening) on the monitoring server. They stated that ALL messages from ANY monitoring server that could send e-mail to both internal and external domains be passed through the only allowable 'message/relay' server, which is already configured and running SSL/TLS encryption and registered with a DNS A, MX and PTR record.

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