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This active check sends out special E-Mails to a defined mail address using the SMTP protocol and then tries to receive these |
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emails back by querying the inbox of |
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an IMAP or POP3 mailbox. With this check, you can verify that your whole mail delivery progress is working. |
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| colour | Green |
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| title | LAST TESTED ON CHECKMK 2.3.0P1 |
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| borderColor | black |
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| bgColor | #f8f8f8 |
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| title | Table of Contents |
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Step-by-step guide
- WATO - CONFIGURATION → Host & Service Parameters → Active checks Setup → Services → HTTP, TCP, Email, ... → Check Email Delivery Check Email Delivery
- Name:
- Subject
SMTP Server→ 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 authentification- 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
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: Your credentials for the SMTP Server
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- 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
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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
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.
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.png?version=1&modificationDate=1735827359413&cacheVersion=1&api=v2&width=1200 "Screenshot of where to locate the service check command within the screen.")
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| language | bash |
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| theme | RDark |
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| title | ~/lib/nagios/plugins |
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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'
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For a detailed log, you can use --debug at the end of the command:
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| language | bash |
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| theme | RDark |
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| title | ~/lib/nagios/plugins |
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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' --debug |
For more information, you can use --help option:
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~/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.
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| language | bash |
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| theme | RDark |
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| title | ~/var/check_mk |
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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
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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'.
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--debug --status-dir /tmp --status-suffix TEST |
With this option, you will save the State-File in /tmp with the Suffix 'TEST'
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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 |
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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):
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root@mylinuxhost:~# openssl s_client -crlf -connect imap.gmail.com:993 |
Which should give you something like this:
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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
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read R BLOCK
* OK Gimap ready for requests from 87.132.243.59 i15mb422427011wre |
And you can log in via
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tag login <username> <password> |
You can also use nmap for further debugging:
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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:
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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.
Related articles
| Filter by label (Content by label) |
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| spaces | KB |
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| showSpace | false |
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| reverse | true |
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| type | page |
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| cql | label in ( "email" , "check_mail_loop" , "emailloop" , "active_check" ) and type = "page" and space = "KB" |
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