DISCLAIMER - ABANDONED/UNMAINTAINED CODE / DO NOT USE

While this repository has been inactive for some time, this formal notice, issued on December 10, 2024, serves as the official declaration to clarify the situation. Consequently, this repository and all associated resources (including related projects, code, documentation, and distributed packages such as Docker images, PyPI packages, etc.) are now explicitly declared unmaintained and abandoned.

I would like to remind everyone that this project’s free license has always been based on the principle that the software is provided "AS-IS", without any warranty or expectation of liability or maintenance from the maintainer. As such, it is used solely at the user's own risk, with no warranty or liability from the maintainer, including but not limited to any damages arising from its use.

Due to the enactment of the Cyber Resilience Act (EU Regulation 2024/2847), which significantly alters the regulatory framework, including penalties of up to €15M, combined with its demands for unpaid and indefinite liability, it has become untenable for me to continue maintaining all my Open Source Projects as a natural person. The new regulations impose personal liability risks and create an unacceptable burden, regardless of my personal situation now or in the future, particularly when the work is done voluntarily and without compensation.

No further technical support, updates (including security patches), or maintenance, of any kind, will be provided.

These resources may remain online, but solely for public archiving, documentation, and educational purposes.

Users are strongly advised not to use these resources in any active or production-related projects, and to seek alternative solutions that comply with the new legal requirements (EU CRA).

Using these resources outside of these contexts is strictly prohibited and is done at your own risk.

Regarding the potential transfer of the project to another entity, discussions are ongoing, but no final decision has been made yet. As a last resort, if the project and its associated resources are not transferred, I may begin removing any published resources related to this project (e.g., from PyPI, Docker Hub, GitHub, etc.) starting March 15, 2025, especially if the CRA’s risks remain disproportionate.

WIP - Use with caution. You can delete your mails!

check_email

Table of Contents

1. About
2. License
3. Usage
4. Configuration
5. Thanks
6. Contributing

About

check_email is a plugin to monitor email transmissions. It sends an email via SMTP to a given email-address and evaluates the email receipt via IMAP. Furthermore check_email can handle echo replies. An echo reply or in other name echo-mail will be sent from a mail server, which received an email and responds to it. The last feature which check_email offers, is a cleanup option. This allows to delete mails, which were sent by check_email or the echo reply.

License

This plugin is licensed under the terms of the GNU General Public License Version 2, you will find a copy of this license in the LICENSE file included in the source package.

Usage

Send an email and check for its delivery

In order to send an email to a given IMAP server and check for its delivery, you have to set the required arguments (see the example below). The plugin sends an email with an unique (hash) subject and X-Custom-Tag via SMTP to the specified email-address. Afterwards the plugin connects via IMAP to the given mail account and searches in the given mailbox for the email sent before. Dependent on the thresholds, the plugin searches through the mailbox until the critical threshold is exceeded.

Required arguments:
      --imap-host=[IMAP_HOST]
      --imap-port=[IMAP_PORT]
      --imap-user=[IMAP_USERNAME]
      --imap-password=[IMAP_PASSWORD]
      --smtp-host=[SMTP_HOST]
      --smtp-port=[SMTP_PORT]
      --smtp-user=[SMTP_USERNAME]
      --smtp-password=[SMTP_PASSWORD]
      --sender=[SENDER_ADDRESS]
      --receiver=[RECEIVER_ADDRESS]

If not otherwise specified, the default values will be applied:
      --imap-port=993
      --imap-mailbox='INBOX'
      --smtp-port=465
      --critical=500
      --warning=300

Check for echo replies

If the argument --echo-reply is set, the plugin assumes that an echo-mail will be send automatically from a mail server, to inform the sender of the previous sent email that the email has been delivered. Therefore, the plugin searches for this specified echo-mail in the mailbox of the sender account via IMAP. Usually the echo-mail subject contains the same subject as the previous sent email e.g.: “RE: Subject”

NOTE: This echo function has to be configured on the mail server.

Required arguments:
      --echo-reply

If not otherwise specified, the default values will be applied:
      --imap-sender-host=[--smtp-host]
      --imap-sender-port=993
      --imap-sender-mailbox='INBOX'
      --imap-sender-user=[--smtp-user]
      --imap-sender-password=[--smtp-password]
      --critical-reply=500
      --warning-reply=300

Cleanup

In order to avoid a full mailbox of echo-mails and check-mails, there is an argument --cleanup to delete echo-mails and check-mails.

Use this option with caution, it could delete involuntary emails if the wrong --imap-mailbox, --imap-sender-mailbox or --reply-name is specified!

Required arguments:
      --cleanup
      --reply-name=[REPLY_NAME]

If not otherwise specified, the default values will be applied:
      --cleanup-time=3600

Optional: environment variables

Check_email can gather these following environment variables from the system:

export IMAP_USERNAME='username'
export IMAP_PASSWORD='password'
export SMTP_USERNAME='username'
export SMTP_PASSWORD='password'
export IMAP_SENDER_USERNAME='username'
export IMAP_SENDER_PASSWORD='password'

NOTE: It's currently not implemented to define more than one of each SMTP, IMAP and IMAP_SENDER

Example - Send an email and check for its delivery (without cleanup)

./check_mail.py \
		--smtp-host='mail.example.com' \
		--smtp-port=587 \
		--smtp-user='DOMAIN\User' \
		--smtp-password='***' \
		--sender='sender@example.com' \
		--imap-host='imap.example.com' \
		--imap-port=993 \
		--imap-user='receiver@example.de' \
		--imap-password='***' \
		--receiver='receiver@example.de' \
		--imap-mailbox='Monitoring' \
		--warning=300 \
		--critical=500

1. The plugin connects to mail.example.com, creates an unique hash subject and sends an email to receiver@example.com
2. The plugin connects to imap.example.com, searches trough the mailbox Monitoring
3. If the email cannot be found within 300 seconds, the return state will be WARNING
4. After 500 seconds, the plugin will exit and return a CRITICAL

Output - Send an email and check for its delivery (without cleanup)

OK - check_email: imap.example.com - Email received in 3s | 'receive'=3

The email was found, and the plugin returns OK. Additionally, the duration how long this action took will be served as perfdata.

Example - Check for echo replies (with cleanup)

./check_mail.py \
		--smtp-host='mail.example.com' \
		--smtp-port=587 \
		--smtp-user='DOMAIN\User' \
		--smtp-password='***' \
		--sender='sender@example.com' \
		--imap-host='imap.example.com' \
		--imap-port=993 \
		--imap-user='DOMAIN\User' \
		--imap-password='***'\
		--receiver='receiver@example.com' \
		--imap-mailbox='Monitoring' \
		--warning=300 \
		--critical=500 \
		--echo-reply \
		--imap-sender-host='imap.sender.example.com' \
		--imap-sender-port=993 \
		--imap-sender-user='DOMAIN\User' \
		--imap-sender-password='***' \
		--imap-sender-mailbox='Monitoring' \
		--reply-name='Echo Notify' \
		--warning-reply=300 \
		--critical-reply=500 \
		--cleanup \
		--cleanup-time=300

1. The plugin connects to mail.example.com, creates an unique hash subject and sends an email to receiver@example.com.
2. The plugin connects to imap.example.com, searches trough the mailbox Monitoring. Additionally, emails with the X-Custom-Tag and if they are older then 300 seconds, will be deleted.
3. If the email cannot be found within 300 seconds, the state will be WARNING
4. After 500 seconds the plugin will exit and return a CRITICAL
5. If the email was found, the plugin connects to imap.sender.example.com
6. The plugin selects the mailbox Monitoring and searches for the assumend echo-mail, which should contain Echo Notify in the subject. Additionally, old echo-mails will be deleted (see 2.)
7. If the echo-mail cannot be found within 300 seconds, the return state will be WARNING
8. After 500 seconds, the plugin will exit and return a CRITICAL

Output - Email loop example with cleanup

OK - check_email: Email loop took 7s | 'receive'=3 'reply'=4 'loop'=7

The sent-mail and echo-mail was found and the plugin returns OK. Additionally, the duration how long each action took will be served as perfdata.

NOTE: The output will be always the highest state, e.g.: receive is WARNING and reply is, the plugin output will be WARNING.

Configuration

Icinga

IMPORTANT check_timeout must be greater than the critical threshold otherwise the default timeout of a plugin could be exceeded and Icinga kills its process. As a result, the plugin can never reach the critical state. Moreover check_interval has also to be lower than the check_timeout. Due to the fact, that the plugin waits for an email or rather an event, the execution time could be, in the worst case, higher than the check_interval. In such circumstances Icinga triggers check_email again, even if the plugin did not finish correctly.

See check_email.conf for an example configuration

Mail server

It is recommended to configure rules to manage emails from this plugin. By using a rule, any received email message that match conditions specified in the rule can be automatically forwarded or redirected to another mailbox (of the same account!). This is very useful, since the plugin searches through a given mailbox. It could be a negative impact if the specified mailbox is filled up with other mails, which are also be evaluated.

Thanks

• Michael Friedrich
• Markus Frosch
• Markus Waldmüller

Contributing

There are many ways to contribute to check_email -- whether it be sending patches, testing, reporting bugs, or reviewing and updating the documentation. Every contribution is appreciated!