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Info

This active check sends out special E-Mails to a defined mail address using the SMTP protocol and then tries to receive these

...

emails back by querying the inbox of

...

an IMAP or POP3 mailbox. With this check, you can verify that your whole mail delivery progress is working.

Status
colourGreen
titleLAST TESTED ON CHECKMK 2.3.0P1


Panel
borderColorblack
bgColor#f8f8f8
titleTable of Contents

Table of Contents

Step-by-step guide

  1. WATO - CONFIGURATION → Host & Service Parameters → Active checks Setup → Services → HTTP, TCP, Email, ... → Check Email Delivery Check Email Delivery→ Add Rule

    • Name: The service description will be Mail Loop plus this name
    • Subject: Here, you can specify the subject text instead of the default text 'Check_MK-Mail-Loop'.
    • SMTP Server: You can specify a hostname or IP address different from the IP address of the host this check will be assigned to.
    • Use TLS over SMTP: Encrypt SMTP communication using TLS
    • Use TLS for IMAP authentication: IMAP
    authentification
    • authentication uses TLS
    • SMTP TCP Port to connect to: The TCP Port the SMTP server is listening on. Defaulting to 25.

    • SMTP Authentication:  Your credentials for the SMTP Server

    InfoImage Removed


    • Screenshot of Check email delivery. Information provided for Name, subject, smtp server. TLS over smtp enabled. Smtp authenication enabled.Image Added


    • Mail Receiving
      • IMAP/POP3: Chose whether you want to use IMAP or POP3
      • IMAP Server: You can specify a hostname or IP address different from the IP address of the host this check will be assigned to.
      • SSL Encryption: Encrypt IMAP communication using TLS
      • Authentication: Your credentials for the IMAP Server
    • From: email address

    • Destination: email address

    • Connect Timeout: Timeout in seconds for network connects (defaults to 10)
    • Loop duration: Loop duration of the most recent mail in seconds or the average of all received
    mails
    • emails within a single check to raise a WARNING/CRITICAL state

    • Delete processed messages: Delete all messages identified as being related to this check plugin. This is disabled by default, which might make your mailbox grow when you do not clean it up manually.

    InfoImage Removed


    • Screenshot of Check email delivery. Mail reveiving set to IMAP. Image Added


Debugging

Execute active Check manually

or For debugging reasons, it could be useful helpful to run the check manually. Therefore, you need to open the service site of the E-Mail service and search for 'Service check command'. Now you can use the command for executing the check manually.

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Screenshot of Mail loop email delivery checkImage Added

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Screenshot of where to locate the service check command within the screen.Image Added



linenumbers
OMD[
nagnis_master
mysite]:~/lib/nagios/plugins$ ./check_mail_loop--pwstore=4@16@provider1,10@17@provider2 '--smtp-server=smtp.provider1.
de
com' '--smtp-tls' '--smtp-username=
mail@provider1
user@provider1.
de
com' '--smtp-password=*************' '--fetch-protocol=IMAP' '--fetch-server=imap.provider2.
de
com' '--fetch-ssl' '--fetch-port=993' '--fetch-username=mail@provider2.
de
com' '--fetch-password=*************' '--mail-from=
mail@provider1
user@provider1.
de
com' '--mail-to=mail@provider2.
de
com' '--delete-messages' '--status-suffix=localhost-Email Delivery' '--warning=120' '--critical=300' '--subject=Check_MK-Mail-Loop for Strato'
Code Block
languagebash
themeRDark
title~/lib/nagios/plugins
true


For a detailed log, you can use --debug at the end of the command:

true
Code Block
languagebash
themeRDark
title~/lib/nagios/plugins
linenumbers
OMD[
nagnis_master
mysite]:~/lib/nagios/plugins$ ./check_mail_loop--pwstore=4@16@provider1,10@17@provider2 '--smtp-server=smtp.provider1.
de
com' '--smtp-tls' '--smtp-username=
mail@provider1
user@provider1.
de
com' '--smtp-password=*************' '--fetch-protocol=IMAP' '--fetch-server=imap.provider2.
de
com' '--fetch-ssl' '--fetch-port=993' '--fetch-username=mail@provider2.
de
com' '--fetch-password=*************' '--mail-from=
mail@provider1
user@provider1.
de
com' '--mail-to=mail@provider2.
de
com' '--delete-messages' '--status-suffix=localhost-Email Delivery' '--warning=120' '--critical=300' '--subject=Check_MK-Mail-Loop for Strato' --debug


For more information, you can use --help option:

Code Block
languagebash
themeRDark
~/lib/nagios/plugins/check_mail_loop -h


Status-File

This plugin needs a file to store information about sent, received, and expected mailsemails. Defaults to either /tmp/ or /omd/sites/<sitename>/var/check_mk when executed from within an OMD site.

Code Block
languagebash
themeRDark
title~/var/check_mk
linenumberstrue
OMD[nagnis_mastermysite]:~/lib/nagios/plugins$ ls -ltr ~/var/check_mk/ |grep 'check_mail'
-rw-rw----  1 nagnis_master nagnis_mastermysite mysite     15 Dec  8 13:12 check_mail_loop.localhost-Email Delivery.status

OMD[nagnis_mastermysite]:~/lib/nagios/plugins$ cat ~/var/check_mk/check_mail_loop.localhost-Email\ Delivery.status 
1607429555 304


For debugging reasons, it may be useful to change the path and suffix of the State-File. You can do this with '--status-dir PATH' and '--status-suffix SUFFIX'.

Code Block
languagebash
themeRDark
--debug --status-dir /tmp --status-suffix TEST


With this option, you will save the State-File in /tmp with the Suffix 'TEST'

Code Block
languagelinenumbersbash
themetrueRDark
OMD[nagnis_mastermysite]:~/lib/nagios/plugins$ ./check_mail_loop --pwstore=4@16@strato,10@17@strato '--smtp-server=smtp.provider1.decom' '--smtp-tls' '--smtp-username=mail@provider1user@provider1.decom' '--smtp-password=*************' '--fetch-protocol=IMAP' '--fetch-server=imap.provider2.decom' '--fetch-ssl' '--fetch-port=993' '--fetch-username=mail@provider2.decom' '--fetch-password=*************' '--mail-from=mail@provider1user@provider1.decom' '--mail-to=mail@provider2.decom' '--delete-messages' '--status-suffix=localhost-Email Delivery' '--warning=120' '--critical=300' '--subject=Check_MK-Mail-Loop for Strato'--debug --status-dir /tmp --status-suffix TEST


MD[nagnis_master
Code Block
linenumberstrue
languagebash
themeRDark
OMD[mysite]:~/lib/nagios/plugins$ ls -ltr /tmp/ |grep 'check_mail'
-rw-rw---- 1 nagnis_master nagnis_master   15 Dec  8 13:21 check_mail_loop.TEST.status


Debugging mail fetching

If you encounter that Checkmk might not fetch mailsemails, you might want to try out if Checkmk is able to connect to the POP/IMAP servers with openssl OpenSSL (in this case Google IMAP):

root@<server>
Code Block
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languagebash
themeRDark
root@mylinuxhost:~# openssl s_client -crlf -connect imap.gmail.com:993

Which should give you something like this: 

Code Block
languagebash
linenumbersthemetrueRDark
00a0 - f7 44 36 73 a1 9d b7 12-8c 3d 91 38 5b ff 13 d6 .D6s.....=.8[...
00b0 - 0d a5 4c 2e 83 54 9b c2-7f c1 aa 20 cd 25 e6 0f ..L..T..... .%..
00c0 - 9a 65 96 9c 33 1c e2 26-78 9c cb 9b 37 83 40 fa .e..3..&x...7.@.
00d0 - a5 94 f8 7c 19 6f 7b 75-ff 53 36 43 0d 72 88 03 ...|.o{u.S6C.r..
00e0 - 9d 66 fe 39 e0 af 4a 75-6d 25 f6 5f .f.9..Jum%._

Start Time: 1649163351
Timeout : 7200 (sec)
Verify return code: 0 (ok)
Extended master secret: no
Max Early Data: 0
---
read R BLOCK
* OK Gimap ready for requests from 87.132.243.59 i15mb422427011wre

And you can logon log in via 

Code Block
languagelinenumbersbash
themetrueRDark
tag login <username> <password>


You can also use nmap for further debugging:

Code Block
languagebash
themeRDark
root@mylinuxhost:~# nmap smtp.server.tld


This command will show open ports, which will help us to identify which port we need to use in Checkmk:

Code Block
languagebash
themeRDark
Starting Nmap 7.80 ( https://nmap.org ) at 2024-12-24 12:44 CET
Nmap scan report for smtp.strato.de (81.169.145.133)
Host is up (0.029s latency).
Other addresses for smtp.strato.de (not scanned): 2a01:238:20a:202:55f0::1133
Not shown: 994 closed ports
PORT STATE SERVICE
135/tcp filtered msrpc
139/tcp filtered netbios-ssn
443/tcp open https
445/tcp filtered microsoft-ds
465/tcp open smtps
587/tcp open submission


More information can be found one Nmap's official site.

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