I'm dealing with a strange situation involving a calendar invite sent through Microsoft 365. A user invited 20 people—15 from our organization and 5 external accounts (like Gmail and others). Most accepted the invite, but one response came from an email address that wasn't included in the original invitation. This address is from a custom domain with minimal DNS configuration, and the email doesn't show up in any message trace except for that acceptance. The domain seems unrelated to the external invitees. I'm suspecting that one of the external accounts might be compromised or maybe has a forwarding rule set up. Does anyone have insights or alternative explanations for this?
2 Answers
It sounds like one of the invitees could have set up an auto-forwarding rule. That could explain the unexpected acceptance if it forwarded to a random address.
Another thought is that it could be a misconfigured alias. Sometimes, if an email client is set up incorrectly, it might reply from an alias instead of the main address, leading to this situation.
True, but this doesn't seem to be a proper mailbox at all. It looks like it might just be a spoofed address from a mailing server.
Yeah, I think that's a strong possibility too. It would definitely cause confusion!