ommail: Mail Output Module

Purpose

This module supports sending syslog messages via mail. Each syslog message is sent via its own mail. Obviously, you will want to apply rigorous filtering, otherwise your mailbox (and mail server) will be heavily spammed. The ommail plugin is primarily meant for alerting users. As such, it is assumed that mails will only be sent in an extremely limited number of cases.

Ommail uses up to two templates, one for the mail body and optionally one for the subject line. Note that the subject line can also be set to a constant text. If neither the subject nor the mail body is provided, a quite meaningless subject line is used and the mail body will be a syslog message just as if it were written to a file. It is expected that the users customizes both messages. In an effort to support cell phones (including SMS gateways), there is an option to turn off the body part at all. This is considered to be useful to send a short alert to a pager-like device. It is highly recommended to use the

action.execonlyonceeveryinterval="<seconds>"

parameter to limit the amount of mails that potentially be generated. With it, mails are sent at most in a <seconds> interval. This may be your life safer. And remember that an hour has 3,600 seconds, so if you would like to receive mails at most once every two hours, include a

action.execonlyonceeveryinterval="7200"

in the action definition. Messages sent more frequently are simply discarded.

Configuration Parameters

Configuration parameters are supported starting with v8.5.0. Earlier v7 and v8 versions did only support legacy parameters.

Caveats/Known Bugs

The current ommail implementation supports SMTP-direct mode only. In that mode, the plugin talks to the mail server via SMTP protocol. No other process is involved. This mode offers best reliability as it is not depending on any external entity except the mail server. Mail server downtime is acceptable if the action is put onto its own action queue, so that it may wait for the SMTP server to come back online. However, the module implements only the bare SMTP essentials. Most importantly, it does not provide any authentication capabilities. So your mail server must be configured to accept incoming mail from ommail without any authentication needs (this may be change in the future as need arises, but you may also be referred to sendmail-mode).

In theory, ommail should also offer a mode where it uses the sendmail utility to send its mail (sendmail-mode). This is somewhat less reliable (because we depend on an entity we do not have close control over - sendmail). It also requires dramatically more system resources, as we need to load the external process (but that should be no problem given the expected infrequent number of calls into this plugin). The big advantage of sendmail mode is that it supports all the bells and whistles of a full-blown SMTP implementation and may even work for local delivery without a SMTP server being present. Sendmail mode will be implemented as need arises. So if you need it, please drop us a line (If nobody does, sendmail mode will probably never be implemented).

Examples

module(load="ommail")

template (name="mailBody"  type="string" string="RSYSLOG Alert\\r\\nmsg='%msg%'")
template (name="mailSubject" type="string" string="disk problem on %hostname%")

if $msg contains "hard disk fatal failure" then {
   action(type="ommail" server="mail.example.net" port="25"
          mailfrom="rsyslog@example.net"
          mailto="operator@example.net"
          subject.template="mailSubject"
          action.execonlyonceeveryinterval="21600")
}

module(load="ommail")

template (name="mailBody"  type="string" string="RSYSLOG Alert\\r\\nmsg='%msg%'")
template (name="mailSubject" type="string" string="disk problem on %hostname%")

if $msg contains "hard disk fatal failure" then {
   action(type="ommail" server="mail.example.net" port="25"
          mailfrom="rsyslog@example.net"
          mailto=["operator@example.net", "admin@example.net"]
          subject.template="mailSubject"
          action.execonlyonceeveryinterval="21600")
}

module(load="ommail")

template (name="mailBody"  type="string" string="RSYSLOG Alert\\r\\nmsg='%msg%'")

if $msg contains "hard disk fatal failure" then {
   action(type="ommail" server="mail.example.net" port="25"
          mailfrom="rsyslog@example.net"
          mailto=["operator@example.net", "admin@example.net"]
          subject.text="rsyslog detected disk problem"
          action.execonlyonceeveryinterval="21600")
}

Additional Resources

A more advanced example plus a discussion on using the email feature inside a reliable system can be found in Rainer’s blogpost “Why is native email capability an advantage for a syslogd?“

Copyright 2008-2023 Rainer Gerhards (Großrinderfeld), and Others.