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= DomainKeys Identified Mail =
'''DomainKeys Identified Mail'''


== Links ==


= Links =
==DKIM checks==
[https://dkimvalidator.com/ DKIMvalidator]
*[http://dkimcore.org/tools/keycheck.html dkim check]  
*[http://dkimcore.org/tools/keycheck.html dkim check]  
*[http://www.myiptest.com/staticpages/index.php/DomainKeys-DKIM-SPF-Validator-test http://www.myiptest.com/staticpages/index.php/DomainKeys-DKIM-SPF-Validator-test]
==DKIM documentation==
*[https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-dkim-with-postfix-on-debian-wheezy DKIM and postfix]  
*[https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-dkim-with-postfix-on-debian-wheezy DKIM and postfix]  
*[https://help.ubuntu.com/community/Postfix/dkim-milter https://help.ubuntu.com/community/Postfix/dkim-milter] Postfix and dkim-milter]  
*[https://help.ubuntu.com/community/Postfix/dkim-milter Postfix and dkim-milter]  
*[http://dkim.org/ DKIM Homepage]
*[https://www.samlogic.net/articles/dkim--cname-or-txt.htm DKIM with CNAME or TXT]
*[http://www.opendkim.org/opendkim-README http://www.opendkim.org/opendkim-README]  
*[http://www.sendmail.com/sm/wp/dkim// About DKIM]  
*[http://www.sendmail.com/sm/wp/dkim// About DKIM]  
*[[DKIM_with_Sendmail|DKIM with Sendmail]]  
*[[DKIM_with_Sendmail|DKIM with Sendmail]]  
*[https://wiki.debian.org/OpenDKIM https://wiki.debian.org/OpenDKIM]  
*[https://wiki.debian.org/OpenDKIM https://wiki.debian.org/OpenDKIM]  
*[http://www.myiptest.com/staticpages/index.php/DomainKeys-DKIM-SPF-Validator-test http://www.myiptest.com/staticpages/index.php/DomainKeys-DKIM-SPF-Validator-test]
*[https://www.linode.com/docs/email/postfix/configure-spf-and-dkim-in-postfix-on-debian-9/ SPF and DKIM on Debian]  
*[https://www.linode.com/docs/email/postfix/configure-spf-and-dkim-in-postfix-on-debian-9/ SPF and DKIM on Debian]  
*[https://tweenpath.net/opendkim-postfix-smtp-relay-server-on-debian-7/  DKIM on relay server]
*[[OpenDKIM]]
 
 
 
 
= OpenDKIM Howto =
 
cd /etc/opendkim/keys
 
The 'selector' you choose here does not have to be the actual selector used in DNS. It is just the name used for storing the .txt and .private files
 
opendkim-genkey -s somename -d domain.name
 
Make sure the key ends up in /etc/opendkim/keys and is readable for user opendkim
 
== SigningTable ==
 
#somename is the first field in Keytable
 
*@domain.name somename
 
== KeyTable ==
 
Here the name of the selector (the part before ._domainkey) is the one you publish in dns
 
somename domain.name:selectorname:/path/to/somename.private
 
==Configuration file /etc/opendkim.conf==
Mode    s
KeyTable        /etc/opendkim/KeyTable
SigningTable    refile:/etc/opendkim/SigningTable
 
== Postfix ==
 
In /etc/postfix/main.cf:
 
 


milter_protocol = 2
*[https://diziet.dreamwidth.org/16025.html dkim key rotation]
milter_default_action = accept
smtpd_milters = inet:localhost:8891
non_smtpd_milters = inet:localhost:8891


 
=DKIM tags=
* https://mxtoolbox.com/dmarc/dkim/dkim-signature-tags


= Checking =


opendkim-testkey -d domain.name -s selectorname -vv -k keys/keyname.private
=Tools=
==dkimverify==


This will try to fetch the key published in DNS, so "record not found" means DNS record not found. No output is good output.
=HOWTO=
==Find published dkim key==
In mailheader look for 'd=' and 's=' to get domain and selector, then
dig <selector>._domainkey.<domain> TXT


*[https://www.dmarcanalyzer.com/nl/dkim-record-validatie/ https://www.dmarcanalyzer.com/nl/dkim-record-validatie/]
==Check if keys match==
dig myselector._domainkey.example.com txt


==WARNING:Unsafe permissions==
and save the bit from "p=" to '''public.key.b64'''
make readable for user opendkim only
You will probably need to remove the quotes/spaces:
| sed 's/[\" \"|\"$]//g'


openssl enc -base64 -d -in public.key.b64 -out public.key
openssl rsa -pubin -inform DER -in public.key -noout -modulus
and compare the shown modulus with
openssl rsa -in private.key -noout -modulus


==keys do not match==
They should be identical
Try
opendkim-testkey -d domain.name -s selectorname -vv


= FAQ =
= FAQ =
== opendkim: no signing table match for ==
In opendkim.conf use:
refile:/etc/opendkim/SigningTable
== opendkim-testkey key not secure ==
Probably means you have no DNSSEC
==opendkim-testkey: keys do not match==
probably means double check Keytable
== opendkim: /etc/opendkim.conf: /etc/opendkim/keys/default.private: open(): No such file or directory ==
Means it's defined in opendkim.conf, and you're not using KeyTable
&nbsp;
== This doesn't seem to be a valid RSA public key: RSA.xs:178: OpenSSL error: bad base64 decode ==
??
[[Category:Mail]]
[[Category:Mail]]

Latest revision as of 07:12, 29 April 2026

DomainKeys Identified Mail


Links

DKIM checks

DKIMvalidator

DKIM documentation

DKIM tags


Tools

dkimverify

HOWTO

Find published dkim key

In mailheader look for 'd=' and 's=' to get domain and selector, then 

dig <selector>._domainkey.<domain> TXT

Check if keys match

dig myselector._domainkey.example.com txt

and save the bit from "p=" to public.key.b64 You will probably need to remove the quotes/spaces: 

| sed 's/[\" \"|\"$]//g' 

openssl enc -base64 -d -in public.key.b64 -out public.key
openssl rsa -pubin -inform DER -in public.key -noout -modulus

and compare the shown modulus with 

openssl rsa -in private.key -noout -modulus

They should be identical

FAQ

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