How will route an email in a coexistent organization?

Copper Contributor

Hi experts,

I hope you're all doing well. :smile:

First of all sorry for the long text.


I have a question about the routing and SMTP primary server which sends the email out of the organization. I read the articles of Microsoft about mail routing and mail flow but I could not find my answer.  :cry:



In my case, I have two Exchange 2013 and two Exchange 2019. I want to complete the migration to Exchange 2019 but have to ensure the Outbound mail flow. 

I have to ensure after I shut down the old servers, the outbound mail flow will continue to work. But what I see now in the message headers of emails that I send out is, that all emails will refer to one of the old servers, then it sends the email as the main SMTP server to the smart host.

I have old servers on an old load balancer which communities with the MX record through the VIP, and set the new servers on a new load balancer that doesn't communicate with MX record through the VIP on the new load balancer. I tried to show in the diagram the structure of the server.


I have just old servers in the send connector and have tested it to add the new ones in the send connector. But still see that emails from test mailboxes on the new servers will first be delivered to one of the old servers and then to the destination out of the organization.




Can someone explain, why all emails are going out through one of the old ones? Or is it important at all? Is it possible that after connecting the new load balancer VIP to the MX record, the transport role decides to send all emails out through the new servers? (also adding new servers to send connector and removing the old ones)


It is confusing for me and I would appreciate any help or tips about it because my migration is stuck in this step because I'm not sure about the outbound mail flow.

Or is this question basically correct? Should I do anything about the mail flow on Exchange servers?


Best Regards,





1 Reply


In Exchange 2013 and later versions, Safetynet is enabled by default and mail is stored on both servers.
Therefore, if the mail is not saved on both servers, the mail will not be transmitted.
Try setting the corresponding safetynet function to off!
Set-transportconfig –ShadowRedundancyEnabled $false