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Chong-7118 asked Chong-7118 commented

Exchange Cross-forest migration when source and target domain use same email address

Hi Support,

We have a AD and exchange 2013 in abc.com and planned to migrate user mailbox to new domain xyz.com. We setup new AD and exchange 2019 in xyz.com, and also setup the ADMT server to migrate AD object from abc.com to xyz.com.

The question is abc.com user account’s primary email address is using xyz.com already (not abc.com), so both user email address in abc.com and xyz.com will be xyz.com. How to configure the connector and exchange server so the email flow can work normally in abc.com and xyz.com coexistence environment

Thanks

Best Regards
Chong

office-exchange-server-administrationoffice-exchange-server-mailflow
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ZhengqiLou-MSFT avatar image
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ZhengqiLou-MSFT answered Chong-7118 commented

Hi @Chong-7118 ,

Here is what I thought:
The Exchange 2013, you use the email address policy to change the mailbox address from abc.com to xyz.com. While the server fqdn was still Https://ex2013.abc.com and all connectors and records were using it.

The Exchange 2019, it's defaultly set to use xyz.com as the mailbox address suffix. The fqdn should be Https://ex2019.xyz.com.

And my questions:
As you said, you have migrated the AD object from abc.com to xyz.com, have you migrated the mailboxes, or only the AD objects?
Two cases:
1. If you only migrated the AD objects, then the Exchange should be a fresh server with no mailboxes and other settings.
2. If you have migrated the mailboxes from 2013 to 2019, then you could set the mail flow to use 2019 server and abandon 2013.

Another question is what do you mean of "so the email flow can work normally in abc.com and xyz.com coexistence environment"? AFAIK the two cross-forest servers are not able to work together. And for your case, as the mailboxes in abc.com is using xyz.com as it's email address( added as accepted domain I guess), then you shouldn't use it again in 2019 for internet email flow.

I think the best idea should be a full migration and after that you can configure the mail flow settings. And also, please provide more details if I didn't understand your questions correctly:)

Have a nice day!

Best regards,
Lou


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Hi @ZhengqiLou-MSFT ,

Thanks for your reply.

  1. Yes. We will perform the domain migration from abc.com to xyz.com. So both user account and the mailbox will migration to the xyz.com domain. User and other AD object will migrated by ADMT, and mailbox will cross-forest migration

  2. My meaning is: As both domain user email address is xyz.com, we need to make sure all user can send and receive internal and external email, no matter they locate in abc.com, or migrated to xyz.com. (It should use xyz.com in new domain as this is business requirement)

I think both exchange 2013 and 2019 should configure xyz.com to “internal relay” in accepted domain.

For the connector, if the email address is different, we can just configure the target address route to target exchange server. But as they are same email address, I don’t know can they route between 2 domain (the MX record can point to either 2013 and 2019)

Thanks


Best Regards
Chong

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Hi @Chong-7118 ,

Thanks for the details, that lets me know more about your questions.

Yes you could configure the xyz.com as the internal relay domain and create a send connector for it.

See this post: https://practical365.com/how-to-share-an-email-domain-between-two-mail-systems/
Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

And remember to disable recipient lookup by Set-AcceptedDomain XXX -AddressBookEnabled $False.
https://docs.microsoft.com/en-us/exchange/mail-flow/accepted-domains/accepted-domains?view=exchserver-2019#recipient-lookup-in-accepted-domains

Again, kindly suggest you to consider a full migration while not use the above methods. Only when you want to keep both server running:)

Best regards,
Lou

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Hi @ZhengqiLou-MSFT ,

Thanks for the information again.

BTW, what is full migration? Can you explain more?
As I said, we will perform the domain migration by ADMT. I will migrate all user/groups/contact/etc from abc.com to xyz.com. Since the ADMT cannot migrate mailbox so we planned to perform the cross-forest mailbox migration.
i
Thanks

Best Regards
Chong

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