Problem
Whenever you try to install dkim and Postfix without cpanel, you have to face the error on configuring DNS record (BIND):
opendkim-testkey: key not found
or
opendkim-testkey: unknown key
Solution
to cut long story short, to store the longer text on a DNS record (i.e Bind9 or Bind), we need to split the data into rows with brackets "( ... )" and quotes ("...") and store it sequentially on different lines. The notation makes me more confusing, just let's see in the example:
default._domainkey IN TXT ("v=DKIM1; h=sha256; k=rsa;"
"p=HalfOfTheKeyHereHalfOfTheKeyHereHalfOfTheKeyHere"
"andAnotherHalfHereAnotherHalfHereAnotherHalfHereAnother")
this key is using 3 consecutive lines.
Testing
you can directly test the configuration from DKIM
opendkim-testkey -d your-domain-name -s default -vvv
this will show that the OK result.
Additional
you can check the consistency of DNS using this command, please change your-domain-name with your appropriate domain name or as your settings on bind dns zones
named-checkzone default._domainkey.your-domain-name db.your-domain-name
