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Configuring Nagios to send e-mail through external Postfix server

Posted on 2010-11-30
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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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Question by:Michael W
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by:Deepak Kosaraju
ID: 34239903
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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by:Deepak Kosaraju
ID: 34239918
Oh sorry my bad i should have read the complete question.
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by:Sanga Collins
ID: 34243215
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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by:Sanga Collins
ID: 34243240
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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by:Michael W
ID: 34243342
@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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by:Sanga Collins
ID: 34243426
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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by:Sanga Collins
ID: 34243491
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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by:Deepak Kosaraju
ID: 34243525
@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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by:Michael W
ID: 34264019
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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Sanga Collins earned 500 total points
ID: 34264040
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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