When I send a multipart email from my server to outlook.com, but have it forwarded to a Gmail account (or anywhere else), DKIM fails, with the message "body hash did not verify", even though as far as I can tell the body looks identical to when I send the same message to Gmail directly, and copy-and-pasting the body part and doing a diff yields no differences as well. I have
relaxed/relaxed verification, so whitespaces shouldn't be an issue.
I have no problem with any other email provider forwarding my messages, and if I send a plain text only email to outlook and have it forwarded, I have no problems.
Anyone have any idea what might be going on here? Is this a known issue with outlook.com? (I know it was when DKIM was new, but its been years now, is it possible Microsoft still hasn't fixed it?)