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Question DKIM for Domains not managed by Plesk

mborsig

New Pleskian
Server operating system version
Almalinux 8
Plesk version and microupdate number
18.0.71 U2
Hello all,
I searched a lot, found really nothing, so I'd like to ask here and hope that somebody can help me with an idea.

Short version:
I want to add domains on a pleask server for sending mail with DKIM signature - but they shouldn't be added or managed via Plesk. Plesk is using qmail.
Sending the mails for these domains works fine, but only without DKIM. Keys are created in /etc/domainkeys, what do I have to add for the domains so that they get a DKIM signature?

Longer version:
I have multiple pleask servers, all with qmail. The users at these servers should have one mailserver for sending and receiving mail, lets say mail.centralserver.com. This mailserver runs on a second IP address on one of the Plesk servers. It's using nginx as proxy for IMAP, POP and SMTP. Mailboxes are on the plesk servers where users domains are managed. IMAP and POP3 are authenticated on the central mailserver, then the connection is proxied via nginx to the correct plesk server. If a user sends mails via SMTP, central mailserver is doing SMTP-Auth agains the correct Plesk server where the users domain is really hosted. This can be the server where the central mailserver is running or any other of the plesk servers. If this authentication is successful, nginx takes the users mail and sends it via the installed qmail on localhost. It's going to the outbound queue and is sent. The Plesk server where this nginx mailproxy is running didn't know anything about that procedure. This is working perfectly since years.
Now all these messages should be DKIM signed. This is easy with domains on all the plesk servers, but not on the central mailserver. If a user has it's domain on the same pleask server as the central mailserver nginx proxy is running, all is fine. Message is DKIM signed and sent via the nginx proxy. But if a user from any other connected plesk server sends mail, the mail is sent, but didn't get a DKIM signature. I already added the DKIM keys for all domains from all plesk servers in /etc/domainkeys, but without success. So the question ist, where do I have to add all the domains from all servers that are using the central mailserver to have them DKIM signed?

Any idea is highly appreciated.

Thanks & Greetings
 
The way you have things configured is not a supported method. Since you're using qmail I would recommend that you review Configuring DKIM for qmail and since you've already copied the keys over to /etc/domainkeys, you can skip down to the section titled "Configuring qmail-remote for signing and qmail-smtpd for verification" and you can refer to the settings on the main server that is working for proper settings. Just be warn, as I've mention, this is not a supported method and you would need to do great testing to make sure things functions the way you're expecting.
 
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