I've got magento 2.3 running on apache with php 7.2. I've got email going out through postfix. I'm trying to get DKIM set up using opendkim. The issue i'm seeing is that emails with html formatting (such as the out-of-the-box newsletter subscription confirmation) email fail the DKIM check on the receiving end with the error "body hash did not verify". I can generate simple text-only emails using the newsletter feature in Magento and those go out and get signed without issue. I'm suspecting the issue is related to something splitting long lines somewhere around 998 characters. I believe perhaps this long line length is causing issues with openDKIM. I'm trying to figure out where this line splitting is occurring so I can throttle it back to around 900 characters.
Any ideas oh what could be going on are helpful. Maybe i'm barking up the wrong tree with the line length thing.