We're experiencing an issue with a sender using Mimecast to email our Office 365 tenant. Despite having published MX records, it seems Mimecast is ignoring them and sending emails directly to our Office 365, which causes these messages to get quarantined due to internal transport rules. I'm curious why Mimecast would bypass the MX records we've set up and what can be done to resolve this?
2 Answers
You might want to look at the Mimecast support article regarding Microsoft 365 setups. There are specific processes they recommend to ensure the right routing of emails. A few of our clients faced similar issues until we locked down their setups properly.
It sounds like they might not be using Office 365 properly or something's off in their setup. Sometimes message attribution can get tricky. Have you checked how the emails are flowing? It could be a service misconfiguration on their end.
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