Check Email Delivery (check_mail_loop)

This active check sends out special E-Mails to a defined mail address using the SMTP protocol and then tries to receive these mails back by querying the inbox of a IMAP or POP3 mailbox. With this check you can verify that your whole mail delivery progress is working.

Step-by-step guide

1. WATO - CONFIGURATION → Host & Service Parameters → Active checks → Check Email Delivery
2. Check Email Delivery
   1. Name: The service description will be Mail Loop plus this name
   2. Subject: Here you can specify the subject text instead of default text 'Check_MK-Mail-Loop'.
   3. SMTP Server: You can specify a hostname or IP address different from the IP address of the host this check will be assigned to.
   4. Use TLS over SMTP: Encrypt SMTP communication using TLS
   5. Use TLS for IMAP authentication: IMAP authentification uses TLS
      
   6. SMTP TCP Port to connect to: The TCP Port the SMTP server is listening on. Defaulting to 25.
      

   7. SMTP Authentication:  Your credentials for the SMTP Server
      

      

   8. 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
         
   9. From: email address

   10. Destination: email address

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

   13. 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 not clean it up manually.

       

       
       

Debugging

Execute active Check manually

or debugging reasons it could be useful 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.

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

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

~/lib/nagios/plugins/check_mail_loop -h

Status-File

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

OMD[nagnis_master]:~/lib/nagios/plugins$ ls -ltr ~/var/check_mk/ |grep 'check_mail'
-rw-rw----  1 nagnis_master nagnis_master     15 Dec  8 13:12 check_mail_loop.localhost-Email Delivery.status
OMD[nagnis_master]:~/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_master]:~/lib/nagios/plugins$ ./check_mail_loop --pwstore=4@16@strato,10@17@strato '--smtp-server=smtp.provider1.de' '--smtp-tls' '--smtp-username=mail@provider1.de' '--smtp-password=*************' '--fetch-protocol=IMAP' '--fetch-server=imap.provider2.de' '--fetch-ssl' '--fetch-port=993' '--fetch-username=mail@provider2.de' '--fetch-password=*************' '--mail-from=mail@provider1.de' '--mail-to=mail@provider2.de' '--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]:~/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 mails, 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@<server>:~# 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 via 

tag login <username> <password>

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