DKIM for additional domains (on older cPanel servers)

#1

Hello

My primary domain is mxroute.com.

I registered an additional mxlogin.com as a new domain in my account and entered mxlogin (.mxroute.com) in the sub domain.

When I enable DKIM

default._domainkey 14400 IN TXT
default._domainkey.mxlogin 14400 IN TXT
Two DNS records are shown.

When you register DKIM,

default._domainkey is successful in mxroute.com.

However
If I set default._domainkey on mxlogin.com to the value of default._domainkey, I get a bad RSA signature.
Also, when I set default._domainkey on mxlogin.com to the value of default._domainkey.mxlogin, I get a bad RSA signature.

How can I configure DKIM with an additional domain, mxlogin.com?

#3

I kept receiving DKIM error when testing using mail-tester. I tried to check the value of DKIM, it seem cpanel added " in the middle of it. After carefully remove the " and space behind it, my DKIM working like a charm.

#2

Each domain has it’s own DKIM key. It sounds like you’re on a cPanel server as those use the default._domainkey selector. In that case you’ll need to do a DNS query against that cPanel server for each domain you use DKIM on.

So if you have domain1.com on eagle.mxlogin.com and domain2.com on ghost.mxroute.com, you’ll need these two queries to get your DKIM keys:

dig TXT default._domainkey.domain1.com @eagle.mxlogin.com
dig TXT default._domainkey.domain2.com @ghost.mxroute.com

Note that just copying and pasting these is not the only step, you’ll need to carefully follow the guide in cPanel. The UX for this is terrible and comes with a high risk of user error, which I cannot easily eyeball by request. For that reason I put at the top of the guide that you’re pretty much on your own using DKIM in cPanel, I’ve given up on it long ago as I didn’t want to spend all day every day trying to walk customers through the horrible UX. It’s better to have DKIM disabled than wrong, and since DKIM isn’t a huge addition in and of itself I’ve always recommended to cPanel customers that they leave it off.