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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 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
     

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   • Mail Receiving
     1. IMAP/POP3: Chose whether you want to use IMAP or POP3
        
     2. IMAP Server: You can specify a hostname or IP address different from the IP address of the host this check will be assigned to.
        
     3. SSL Encryption: Encrypt IMAP communication using TLS
        
     4. 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.
     

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Debugging

Execute active Check manually

or 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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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:

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 mailsemails. Defaults to either /tmp/ or /omd/sites/<sitename>/var/check_mk when executed from within an OMD site.

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'.

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

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

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

MDOMD[nagnis_mastermysite]:~/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

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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>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 logon log in via 

tag login <username> <password>

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