Am 11.04.2018 um 16:07 schrieb Ivan Kovachev via dmarc-discuss: > Hello guys, > > I have three questions for you that I am unsure about and hoping that someone > at Microsoft will be able to help: > > First two questions are related to Mimecast acting as inbound security > gateway to O365: > > 1. When Mimecast acts as inbound gateway solution and it receives an email, > it does DMARC checks and lets the email through to O365 environment. Even if > an email passes DMARC checks at Mimecast and the email is let through, then > O365 also seems to also be doing DMARC checks but both SPF and DKIM fail > because of the change that Mimecast does. As a results DMARC fails. My > questions is, what is the best practice here in this scenario? Is there a way > to turn off DMARC checks at O365? Mimecast suggest that it is whitelisted in > O365 but that means that all the spam will be let through as well.
Hello Ivan, I'm unrelated to the companies but had a similar issue. A customer use a domain hosted at Mimecast and forward to us. DMARC validation failed for a portion of messages sent from p=reject domains. I had to disable "reject on DMARC fail" for the servers sending from Mimecast to us. That's fragile as Mimecast may change them at any time. Andreas _______________________________________________ dmarc-discuss mailing list firstname.lastname@example.org http://www.dmarc.org/mailman/listinfo/dmarc-discuss NOTE: Participating in this list means you agree to the DMARC Note Well terms (http://www.dmarc.org/note_well.html)