Forum Discussion
SPF, DKIM and DMARC bypassed for guest users
I manage a small non-profit using Microsoft 365 Business Basic. Most of the people on our board of directors are added as unlicensed guest users so that they can participate in Teams chats and meetin...
Can you share an example NDR/headers?
Guest users do have a matching recipient object (Mail user/Guest mail user) within Exchange Online and so messages will be "resolved" to it first, then send to where the ExternalEmailAddress points at. This however should not result in bypassing SPF and such, unless you have some fancy routing configured, or the message passes through multiple other MTAs before reaching the recipient.
I've tried to reply three times without success. First with headers as text (that failed immediately), then with links to the headers on OneDrive (moderation black hole), and finally with headers as screenshots (another moderation black hole). If there's a trick to posting a reply with email headers, let me know.