I'm trying to send DKIM signed messages from my server in domain ABC.com, to a remote mail server with domain XYZ.com.
- When I send with a FROM address @abc.com the messages arrive to the xyz.com mailbox DKIM signed.
- When I send with a FROM address @somerand.com the messages arrive to the xyz.com mailbox DKIM signed.
- Now when I send with a FROM address of @xyz.com the messages do arrive to the xyz.com mail system, but they are not DKIM signed.
- If I send with a FROM address of @xyz.com and send to DKIMValidator.com, the message is DKIM signed.
Can anyone explain in detail the step by step process? My basic understanding is the MTA will DKIM sign the message if instructed to do so for that queue/domain and attempt to send. Is there any initial communication between the two servers before the DKIM signing takes place, such that a remote domain response could prevent the DKIM signing?