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Configuring Check Email Delivery (check_mail_loop)

Configuring Check Email Delivery (check_mail_loop)

This check sends test emails via SMTP and retrieves them via IMAP/POP3 to verify mail delivery.

LAST TESTED ON CHECKMK 2.3.0P1

Table of Contents

Step-by-step guide

  1. Setup → Services → HTTP, TCP, Email, ... → 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 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



    • 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 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.

 

Debugging

Execute active Check manually

For debugging reasons, it could be 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.







~/lib/nagios/plugins

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

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


~/lib/nagios/plugins

OMD[mysite]:~/lib/nagios/plugins$ ./check_mail_loop--pwstore=4@16@provider1,10@17@provider2 '--smtp-server=smtp.provider1.com' '--smtp-tls' '--smtp-username=user@provider1.com' '--smtp-password=*************' '--fetch-protocol=IMAP' '--fetch-server=imap.provider2.com' '--fetch-ssl' '--fetch-port=993' '--fetch-username=mail@provider2.com' '--fetch-password=*************' '--mail-from=user@provider1.com' '--mail-to=mail@provider2.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:

~/lib/nagios/plugins/check_mail_loop -h

 

Status-File

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


~/var/check_mk

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

--debug --status-dir /tmp --status-suffix TEST

 

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

OMD[mysite]:~/lib/nagios/plugins$ ./check_mail_loop --pwstore=4@16@strato,10@17@strato '--smtp-server=smtp.provider1.com' '--smtp-tls' '--smtp-username=user@provider1.com' '--smtp-password=*************' '--fetch-protocol=IMAP' '--fetch-server=imap.provider2.com' '--fetch-ssl' '--fetch-port=993' '--fetch-username=mail@provider2.com' '--fetch-password=*************' '--mail-from=user@provider1.com' '--mail-to=mail@provider2.com' '--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

 

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 emails, you might want to try out if Checkmk is able to connect to the POP/IMAP servers with OpenSSL (in this case Google IMAP):

root@mylinuxhost:~$ openssl s_client -crlf -connect imap.gmail.com:993

 

Which should give you something like this: 

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 log in via 

tag login <username> <password>

 

You can also use nmap for further debugging:

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:

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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