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Hi, we are running Exchange 2013 and 2019 in a coexistent state. All works great so far.
We are testing something specific today:
Our Exchange 2019 has a tool that handles auto-replies for certain mailboxes.
Email from the internet is always pointed to the IP of the Exchange 2019 server.
When a message comes in from the internet and is delivered to the mailbox by Exchange 2019 the mail touches this auto-reply service and the sender receives a reply.
Some emails however don't receive this auto reply and we now found out that this might be default Microsoft behavior.
Looking at the incoming email headers we can see that some incoming emails are handled by Exchange 2019 and some by Exchange 2013. The signature tool is not installed on 2013 as we are in the proces of removing this server step by step.
To me it seems that Exchange 2019 can loadbalance/offload incoming messages to a different Exchange server in the organization (coexistence?) This causes some emails to bypass the auto-reply service on Exchange 2019... All messages are always delivered into the mailbox it's just that our specific auto-reply is like 50/50 functioning..
Is there any way to safely make sure that Exchange 2019 always processes the incoming message without breaking the mailflow or perfectly functioning coexistent state? We haven't had a single complaint or issue since setting this up
You only have one IP receiving messages from the internet? and that goes to the 2019 server? What is your mx record set to?
Yes email is only received by Exchange 2019.. Port 25 from the outside is only pointing to the 2019 IP adress. But somehow this server offloads some messages to Exchange 2013 first and then Exchange 2013 processes this incoming message and delivers it back to Exchange 2019 where it is then stored in the right mailbox.
It feels like 2019 and 2013 have their own "tunnel" load balancing messages to handle before they are processed thought the transport layers into the mailboxes
Check out these email headers. Two separate emails I send to this mail address. Both sent from outside the company coming into the same mailbox.
EX01 192.168.5.125 is Exchange 2019 (new server)
EX 192.168.5.15 is Exchange 2013 (old server)
The destination mailbox is hosted on 2019...
The upper one got the auto reply though the service on Exchange 2019. The bottom one did not get the auto reply... But both messages were delivered into the target mailbox perfectly fine.
Yea, I think what you are seeing is normal as long as both servers are running.
If you read through:
https://learn.microsoft.com/en-us/exchange/mail-flow/mail-flow?view=exchserver-2019
Specifically:
Yes this seems to be happening. For the outgoing email flow I was able to remove the old Exchange server from the Internet Send connector. This made sure that all outgoing email was always flowing through the new server. (That also applies email signatures to outbound messages)
I was hoping it might be as simple by removing the old server from one of the incoming connectors
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@Caspar I wanted to follow up and know if the below responses helped in answering your query. If it did, please do not forget to accept the appropriate response as Answer so that others in the community facing similar issues can easily find the solution.