Hello,
As of a couple of weeks ago when a member of a distribution group receives an email and is also a recipient of this email they get two copies of the email. Prior to this everything was working normally and they only received one copy of this email. Nothing had changed when this stopped working.
We were on Exchange 2013 CU12 when this started and have now updated to CU14 to see if this is resolved but the issue remains.
I have tried to check the duplicate email detection settings which were in Exchange 2010 but I can't seem to find these in 2013 which is the same as another 2013 server which is working fine.
When we do a message tracking I can see that this email listed twice with the same MessageId, once listed to the recipient and once listed to the individual members of the distribution group.
Has anyone experienced the same issue? Are there any settings I can check with Exchange 2013 to see why this has stopped working? I think I've exhausted browsing Google for the problem.