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Merging multiple email domains after corporate acquisition

I have 3 public email domains that I need to merge due to a corporate merger.  The domains we will call x.com, y.com and z.com.  All email for x.com and y.com need to go to z.com moving forward.  As I understand it, I will need to go to the MX records for the x.com and y.com domains and redirect them to the public IP for z.com and then setup a receive connector to accept x.com and y.com traffic to pick up legacy traffic in the interim.  I also believe that I need to create an email address policy to add the new domain suffixes to the migrated users.

What else am I not thinking about?

Brian Ladley
ExchangeActive DirectoryDNS

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8/22/2022 - Mon
Will Szymkowski

receive connector to accept x.com and y.com traffic to pick up legacy traffic in the interim

You have the right idea about pointing the MX records to z.com public IP for used for mail. The next thing you need to do is not create a receive connector but create an Accepted Domain for x.com and y.com in z.com Exchange environment.

From there you will then create EAP eamil address policies for x.com and y.com. These policies will apply to your users from there respective domains based on specific parameters that you specify OU, or Location etc.

Once that is done you will be able to receive and send as all 3 domains from a single Exchange server.

Aaron Tomosky

Can your internet connection handle the influx of 2 more domains emails?
Can the exchange server handle the load? Storage space? Backups licenses and space? Exchange cals?

Perhaps Use the opportunity to go to office 365.

And think about the order of things....
First enable all new paths... Then propagate them outward.

So you internaly at least had 3 mail servers each receiving stuf.
The first step would be to create forwarding for x.com & y.com from z.com to their respective servers
Then establish z.com as you internal smarthost.

After that you can:
- Migrate mailboxes  x.com & y.com internally to z.com.
- Change the MX records.

And going for office 365, depends on a lot more then just capacity. Are you competing against the supplier of office 365 in some markets? then probably keep away from it. Also geographic spreading might be of influence, and it also depends on being a US citizen or not.
Your help has saved me hundreds of hours of internet surfing.

Thanks for the suggestions to all of you.  The x.com and y.com domains will cease to exist upon completion of the merger.  I am looking into the need for an Active Directory Migration from the other two domains to the z.com domain.

O365 was ruled out by the client due to the nature of the message traffic.  That was one of the first options I considered.

Brian Ladley

Did you consider this about removing x.com & y.com the addresses? They might be in use in a lot of places.
You may want to auto-answer with new addresses to the incoming mails for a while. (with or without forwarding to the original addressee)

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