Exchange migration from 2007 to 2013 different domains used for MX records, would this cause email flow issue

When you have "co-existance" this means that they are working together. What you are trying to accomplish is separate the two servers completely (based on what i have read). Exchange does not work like that.

Typically when you introduce Exchange 2013 into 2007 you want the Newest version of exchange (2013 in this example) to be the primary transport between the Edge Server and internal Exchange. So really all you need to do is NAT your current IP (MX) to the new Exchange 2013 server and all mail will flow into Exchange 2013 and Client Access will also be presented from Exchange 2013 and redirected to 2007 if required.

Based on what you are trying to accomplish I would think you would be trying to create an Exchange Resource Forest and then have them completely separeate and mail will route to each environment respecitively.

You will also need to make sure that your certificates are imported and enabled/configured on your Exchange 2013 environment as well.

Another thing to mention is that if you want to send from a different external IP then you need to make sure that you have an SPF record in place with the other IP added. If you do not do this your Reverse (PTR) record for your MX record will not match up and you will get flagged as spam on the net.


A good reference and high level steps I would recommend using Exchange Server Deployment Assistant.
https://technet.microsoft.com/en-us/office/dn756393.aspx

Will.

Thanks for the reply Will.

I do want the exchange 2013 to be the primary server. We have two certificates one for exchange 2013 (mail.blogs.com) and another for 2007 (mail.contoso.com).

So am I write in assuming that I would need to import the exchange 2007 cert (mail.contoso.com) into exchange 2013 and enable it for SMTP as well as having the current (mail.blogs.com) cert for 2013 already enabled for SMTP?

I have already installed and configured Exchange 2013 into the environment (Edge, CAS and MBX on 3 different servers) but mail flow is only working one direction. I am able to send emails from exchange 2007 and receive them in exchange 2013 but no emails are sending from exchange 2013 to exchange 2007. Not concerned about sending external (internet) email from 2013 at this point.

I've not configured any additional receive or send connectors on 2013 other than the ones that are configured by default (listed below).

receive connectors

Default Frontend MAIL-01
Outbound Proxy Frontend Mail-01
Client Frontend Mail-01
Default Mail-01
Client Proxy Mail-01

Send connectors

EdgeSync - Default-First-Site-Name to Internet
EdgeSync - Inbound to Default-First-Site-Name


thanks