Add DKIM for BlueOnyx VSITE Print

NOTE:  This guide has been obsoleted for BlueOnyx 5210R and 5211R with this feature addition:
http://mail.blueonyx.it/pipermail/blueonyx/2023-January/062970.html

This guide is still effective for BlueOnyx 5209R (BlueOnyx on CentOS 7).

Step 1:  Make new opendkim key directory for the domain

mkdir /etc/opendkim/keys/DOMAIN.TLD

 be sure to substitute the actual domain for DOMAIN.TLD throughout this how-to.

Step 2: Generate the keypair for the domain:

opendkim-genkey -D /etc/opendkim/keys/DOMAIN.TLD -d DOMAIN.TLD -s default

Step 3:   Modify /etc/opendkim/KeyTable

default._domainkey.DOMAIN.TLD DOMAIN.TLD:default:/etc/opendkim/keys/DOMAIN.TLD/default.private

Step 4:  Add the following to /etc/opendkim/SigningTable

*@DOMAIN.TLD default._domainkey.DOMAIN.TLD

Step 5: Ensure ownership of /etc/opendkim is fully owned by opendkim

chown -R opendkim:opendkim /etc/opendkim

Step 6: Restart the opendkim service

systemctl restart opendkim

Step 7:  Restart Sendmail

systemctl restart sendmail

 Step 8:  Add the public key to a DNS txt record for the domain

 Use the text from the file created at /etc/opendkim/keys/DOMAIN.TLD/default.txt and correct for formatting so that it looks like this:

v=DKIM1; k=rsa; p=rh+bZZghwpBE9iDBYKHTo27EOxwZwgPvsj31CbeR/Mgc/gFAqnqT2+LgahYA4NjXj5Huv6XbV51YzFzI5MVoizt9MUbaMIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDjQouvJSFdy6gkT9Lmiivaeb3CX7b​QcsjfAhdV0sZP17Jzupc9MvvGJSdyHEmABMl60Gk/WHL+leJbbQIDAQAB

In other words, remove extraneous spacing and quote marks.

The TXT record should look something like this in the BlueOnyx DNS:

Host Name:   default._domainkey
Domain Name:    DOMAIN.TLD
Text Record:   v=DKIM1; k=rsa; p=rh+bZZghwpBE9iDBYKHTo27EOxw...

Save the record, then save again for the domain.

Step 9:   Test the DNS record using https://www.dmarcanalyzer.com/dkim/dkim-checker/

use "default" as the selector and the new domain.