That sounds normal to me. Exchange is making use of all available transport services in the site.

There’s a diagram here that is a good reference:

https://technet.microsoft.com/en-us/library/aa996349(v=exchg.160).aspx

Also some scenarios like what happens to inbound mail. Note that the front end transport service can proxy the connection to *any* available transport service in the site, it doesn’t necessarily need to be the server hosting the mailbox.

There’s some more detail on routing here:

https://technet.microsoft.com/en-us/library/aa998825(v=exchg.160).aspx

Read the section “Routing in the Front End Transport service on Mailbox servers” to understand the front end transport service behaviour. Also read the section on what constitutes a delivery group.

For outbound, you might be able to change the behaviour by taking the 2013 server out of the source server list for the send connector.

I have this same issue where, after migrating from 2013 to 2016, it seems that when receiving email from an external client (gmail in this instance), the email is received by my smart host, then forwarded as expected to my 2016 server. It is then forwarded back to my 2013 server (which contains no mailboxes anymore), then back to my 2016 server and delivered to mailbox.

When sending to external client, same issue. Exchange 2013 is also still being utilized for mail flow and I don’t know why. Internal email is being used by Exchange 2016 only as far as I can tell.

Paul, I’ve followed your guide on Plurasight with my subscription, but this issue isn’t addressed. Any ideas where to look? I’m just not understanding why 2013 is still involved in mail flow at this point when all DNS records have been changed to 2016, smart host is forwarding to 2016, MX internally was updated to reflect my 2016 server, etc.

Mail is flowing, but why is it using 2013 for external based or external originating emails?

SMTP is forwarding to the 2016 server. (I see some typos in my modified log but the IPs are correct).

I’ve powered down 2013 and mail is flowing well.
I do see some 3008 events that [Owa] failed to refresh mailbox server for database in resource forest.mycool.com and it goes on “Could not connect to Exchange2013.mycool.com” which makes sense as it’s shut down.

The only issue on the client side is a sporadic issue with search on Outlook 2016 – “We’re having trouble fetching results from the server” that just appeared with the 2013 shutdown. I’ve checked and my mailbox indexes on 2016 are all healthy.

I can’t tell from that info why it’s routing to the 2013 server. Looks like inbound mail from an external sender. Is SMTP forwarding from your firewall to the 2013 server or to the 2016 server?

Thank you so much for the series of articles!

Exchange 2013 not decommisioned yet, but mailboxes moved (except for handful of unused ones)

But Exchange 2013 still touches some emails for some reason.

I’ve got two Exchange boxes: 2013 and 2016. No perimeter servers. I am running Symantec Mail Security For Microsoft Exchange and that is on both servers, 2013 and 2016.

Here’s a (names changed) copy of the headers from an email:

Received: from Exchange2013.mycool.com (10.10.1.38) by
Exchange16.mycool.com (10.10.1.58) with Microsoft SMTP Server
(version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id
15.1.1034.26 via Mailbox Transport; Mon, 23 Oct 2017 07:34:26 -0500
Received: from Exchange2016.mycool.com (10.10.1.58) by
Exchange2013.mycool.org (10.10.1.38) with Microsoft SMTP Server (TLS) id
15.0.1293.2; Mon, 23 Oct 2017 07:34:25 -0500
Received: from bounce.aimarketinggrp.com (192.28.148.235) by smtp.mycool.com
(10.10.1.58) with Microsoft SMTP Server (version=TLS1_2,
cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1034.26 via
Frontend Transport; Mon, 23 Oct 2017 07:34:25 -0500

Is it normal for Exchange2016 to toss email over to Exchange 2013 for no real reason? Some kind of load balancing or something going on?

Thank you again!

Running your CAS in the DMZ is not a supported scenario. If you’ve got some DMZ requirements for incoming client traffic then you should look at a reverse proxy or load balancer like an F5, Netscaler, Kemp, etc.

The Edge Transport server is involved in mail flow only. It doesn’t handle any client connectivity for OWA or other client access services.

If the 2016 Edge server is only providing OWA access, do we need an Edge Subscription?