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How do I use OpenDKIM with multiple domain names on a single server?

I own 3 domain names, and I have a single server that's running postfix for sending email. How do I use OpenDKIM?

Can I use the same keyfile for all 3 domain names? Do I have to create a TXT record for each domain name?

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  • Haven't used OpenDKIM (but have used dkim-milter) - I find DKIMProxy to be easier to setup than a milter. In general, you do need a TXT record for every domain that you wish a recipient to verify and you can use the same keyfile for all (although it is preferable for each domain to have its own keyfile). The configuration of OpenDKIM can be found on its site.
    – cyberx86
    Aug 2, 2011 at 4:26

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You'll need to set up a KeyTable with a separate line for each selector/domain/keyfile. It would look like this:

default._domainkey.example1.com example1.com:default:/etc/mail/dkim/keys/example1.com/default
default._domainkey.example2.com example2.com:default:/etc/mail/dkim/keys/example2.com/default
default._domainkey.example3.com example3.com:default:/etc/mail/dkim/keys/example3.com/default

then a SigningTable to determine who can sign on each domain:

*@example1.com default._domainkey.example1.com
*@example2.com default._domainkey.example2.com
*@example3.com default._domainkey.example3.com

Here's an easy How-To for setting it up:

http://stevejenkins.com/blog/2010/09/how-to-get-dkim-domainkeys-identified-mail-working-on-centos-5-5-and-postfix-using-opendkim/

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    Thanks SteveJ! Is it allowed to use the same default.private key for all 3 domains? Or does that invalidate or confuse the authentication process? Mar 30, 2012 at 9:36
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    If you are using subdomains of the same domain, you can just specify Subdomains yes in /etc/opendkim.conf
    – David Xia
    Mar 6, 2013 at 22:59
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    As of January 2022, the linked How-To isn't reachable. Here's a link to a snapshot of the page: web.archive.org/web/20210123113508/https://www.stevejenkins.com/…
    – Pistos
    Jan 20 at 0:43

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