Add DMARC conformity mode (do not modify DKIM signed headers and body)
CRITICAL
I deployed mm3 to my e-mail server working with the large Linux developer community and we are facing DMARC issues [1]. It seems that SMTP servers (mainly gmail.com and outlook.com), are able to handle incoming e-mails from mailing lists but ALL DKIM signatures must pass the verification.
We cannot use any DMARC mitigation - the From and the message body must be preserved for automatic tools. Also, as noted, DMARC can work perfectly without any mitigation when DKIM signatures are correct.
What we found so far:
- CC may be rewritten - workaround in !1039
- Body is modified/reformatted (LF replaced with CR-LF thus DKIM body signature fails) - no fix or workaround yet
A test tool example - dkimverify
- all indexes (including one from the original e-mail) must pass the verification [2].
I can provide test e-mails on demand.