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My present environment is such that the AD domain name is abc.com while the Exchange 2010 email address domain names are @abc.com with @xyz.com as the reply to address. We want to use xyz.com and @xyz.com in the long term.

We want to migrate to O365 using hybrid deployment, should we first migrate AD domain to xyz.com first or is there a shortcut?

Any suggestions will be much appreciated!

Blue Tongue
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  • Follow the steps provided by joeqwerty, you can also refer to this similar case: https://community.spiceworks.com/topic/2108052-azure-ad-connect-different-domain-names – joyceshen Jul 03 '19 at 05:36

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the Exchange 2010 email address domain names are @abc.com with @xyz.com as the reply to address.

I'm assuming that you mean that each user has a user@abc.com email address and a user@xyz.com email address and that the user@xyz.com email address is theur primary SMTP address.

Add and verify xyz.com in your Office 365 tenant. Then add xyz.com as an additional UPN suffix in AD and set that as the UPN Suffix of all your AD user accounts. Then install and configure Azure AD Connect in Hybrid mode in your AD. Once the AD user accounts sync to Azure AD/Office 365 all your Office 365 users will have the UPN of user@xyz.com and will have the primary SMTP address of @xyz.com.

joeqwerty
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  • "I'm assuming that you mean that each user has a user@abc.com email address and a user@xyz.com email address and that the user@xyz.com email address is theur primary SMTP address" - That is correct – Blue Tongue Jul 03 '19 at 00:33
  • "Once the AD user accounts sync to Azure AD/Office 365 ..." - Do you mean that my on-prem AD domain will still be abc.com while the tenant will be @xyz.com? What about the Azure AD which my on-prem AD syncs to? Will there be any ongoing problems? – Blue Tongue Jul 03 '19 at 00:41
  • Your on premises AD will remain as abc.com. Your on premises users will have the UPN suffix of xyz.com. This does not change the on premises domain, it will still be abc.com. Your Azure AD users will have the UPN suffix of xyz.com. This is how Azure AD Connect works so there won't be any problems. – joeqwerty Jul 03 '19 at 11:53
  • Thanks joeqwerty. This brings me up to the next question: fast forward to mailbox migration - that means I have to migrate all mailboxes within a day because @xyz.com cannot point to both on-premises Exchange 2010 and O365 at the same time. Is there a solution to allow me to migrate the mailboxes over a month or so? – Blue Tongue Jul 05 '19 at 01:42
  • You don't have to migrate them all in one day. You'll run the Exchange Hybrid Configuration Wizard on premises and that will connect your on premises Exchange server to your Office 365 Tenant/Exchange Online. Mail will flow between the on premises users and the users that you migrate to Office 365. Your MX record can point to your on premises server or to your Office 365 Tenant/Exchange Online, whichever you prefer. – joeqwerty Jul 05 '19 at 03:35