We have DKIM configured with the MTA we are using with CiviCRM, and it appears to be working. However, the DKIM signature fails consistently; using a checker it appears the mail has been altered after being signed. Has anyone else experience of this?
I've done some more investigation. I have an IIS based development system. Configuring SMTP leads to the test email failing DKIM. Sending a CiviMail test environment passes DKIM. Sending a CiviMail test from Linux Apache based test environment leads to a DKIM failure. Webmail and Thunderbird SMTP both lead to DKIM passes. Any suggestions?