Prevent duplicate emails using Exchange Online Rules

Copper Contributor



First time poster but long time lurker in this forum.


I am in the middle to set my small company Exchange mail flow. One challenge I can't find the solution is to prevent duplicate emails going in to our email servers. I believe some of you guys experience this too. How do you guys handle this? Or is that any way we can make a rules in Exchange to prevent it ?

3 Replies
Old versions of Exchange had a configurable option to detect duplicate messages based on Message-ID and submit time in a limited time window; is that perhaps what you are referring to? As you can imagine, reasons like compliance and the sheer number of messages going through multiple Exchange server environments make this something undesirable or unfeasible (and contrary to shadow redundancy which essentially creates duplicates to counter messages becoming lost in transit)

@Michel de Rooij 


To be honest, I have no idea how to implement your suggestions. For the record, I'm using Exchange Online from Office 365, and I'm usually tinkering on the mail flow > rules section.

Can you elaborate more information for me?


Hes referring to a setting avail in on-prem Exchange:


I dont think Michel was suggesting you make any changes, just pointing out the feature. If you are getting duplicate messages in ExO, then you have a bad process sending those messages or something is broke in ExO and you should open a ticket with 365.