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DKIM not working

hagman_01

I tried to setup DKIM with no success.

1. I used (on my local Linux box) openssl to generate a 1024bit RSA key pair.

2. I added the public key into DNS and let it propagate (for the moment with testing mode "t=y" )

$ host -t txt testing._domainkey.mydomain.example 8.8.8.8
Using domain server:
Name: 8.8.8.8
Address: 8.8.8.8#53
Aliases:

testing._domainkey.mydomain.example descriptive text "v=DKIM1;k=rsa;t=y;p=MIGfMA0......DwIDAQAB"

3. I configured the UTM as follows

Priate key =

-----BEGIN PRIVATE KEY-----
MIIC...
...
...
...
-----END PRIVATE KEY-----

selector = testing

DKIM-Domains = mydomain.example

4. I used https://www.appmaildev.com/en/dkim to check. Result:  DKIM-Result: none (no signature)

Why is no signature added?
According to the result at the receiving end, the mail is from the specified DKIM domain: 

From: "Real Name" <username@domain.example>


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  • 0

    Hello Hagman!

     Thank you for contacting the Sophos Community!

    What is the output of dig nameofthekey._domainkey.domain.com TXT +short

    Regards,

     
    Emmanuel (EmmoSophos)
    Technical Team Lead, Global Community Support
    Sophos Support Videos | Product Documentation  |  @SophosSupport  | Sign up for SMS Alerts
    If a post solves your question use the 'Verify Answer' link.
  • 0 in reply to emmosophos

    "v=DKIM1;k=rsa;t=y;p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDPSj8NGDf71/tmIKyJ3Ymbdgx4IGGxGVQCvj97AhN50uKw6qBpkMNBA8JCz0f4LfyV/2OM7R+WXSKtt/5cQD5mbYQku/5wbjqTJJDMVvBk10TAp636Z/s+zQC9/piaLAzqv/DSnGnxCXAzxK8rxdK5fetzAkf8Iw9vb2ChbbVjDwIDAQAB"

    (cf. the equivalent host command in my post)

    Does that even matter? I mean, a problem with the DNS record would certainly lead to failure in verification of the DKIM signature at the receiving end - but the DKIM signature is not even applied! at my sending end?

    In other words: Does your question mean that UTM does the DKIM signing if it is able to verify that the corresponding public key DNS record (which i dnot needed for the signing per se) is resolvable from the (internal-ish) resolver of the UTM instead of merely from all receiving ends who resolve the "official" version of DNS?

  • 0 in reply to hagman_01

    Hello Hagman,

    Then you would need to check /var/log/smtp.log for one of the outbound emails to see what it says about the signing.

    Regards,

     
    Emmanuel (EmmoSophos)
    Technical Team Lead, Global Community Support
    Sophos Support Videos | Product Documentation  |  @SophosSupport  | Sign up for SMS Alerts
    If a post solves your question use the 'Verify Answer' link.
  • 0 in reply to emmosophos

    At first  thought that no error were logged, but then O found a separate entry

        DKIM: signing failed (RC -101)

    I don't know what that means though (Google only ever heard of RC -102)

  • 0 in reply to hagman_01

    Hello Hagman,

    I was digging for a while but couldn't find anything.

    My guess is that it has to do with the key length, but it is 1024 which should be good enough, I would ask you to create a new one maybe try going higher to 2048.

    If it still fails please open a case with Support to get this investigated further, you can tell them you created a 1024 and a 2048 but it remains the same, also please provide them with the any KB you have followed and the output of the /var/log/smtp.log where it shows that error. 

    Regards,

     
    Emmanuel (EmmoSophos)
    Technical Team Lead, Global Community Support
    Sophos Support Videos | Product Documentation  |  @SophosSupport  | Sign up for SMS Alerts
    If a post solves your question use the 'Verify Answer' link.
Reply
  • 0 in reply to hagman_01

    Hello Hagman,

    I was digging for a while but couldn't find anything.

    My guess is that it has to do with the key length, but it is 1024 which should be good enough, I would ask you to create a new one maybe try going higher to 2048.

    If it still fails please open a case with Support to get this investigated further, you can tell them you created a 1024 and a 2048 but it remains the same, also please provide them with the any KB you have followed and the output of the /var/log/smtp.log where it shows that error. 

    Regards,

     
    Emmanuel (EmmoSophos)
    Technical Team Lead, Global Community Support
    Sophos Support Videos | Product Documentation  |  @SophosSupport  | Sign up for SMS Alerts
    If a post solves your question use the 'Verify Answer' link.
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