Office 365 Hybrid Migration

We are in the beginning stages of setting up our migration from an on premise Exchange 2010 SP3 server to Office 365 hosting.  We have single sign on setup and have setup our Exchange server for the hybrid configuration and federated trust.  We can see all of our users in the Office 365 portal and we can see information flowing between Office 365 and our on-premise server.

We are now at the point where we would like to test move a user's mailbox to the cloud service, however, we are running into a roadblock with regard to the MX record.  It looks like Office 365 is not recognizing our domain as being valid for email since we haven't modified our MX record to point to Office 365.

So, the short question is, do we need to replace our current MX record and insert the new MX pointing to Office 365?  And, if so, will that point all mail to Office 365 (and FOPE) and direct email through the trust for the on-premise mailboxes?
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James HodgeManaging DirectorCommented:
Microsoft prefer it if you use their DNS NameServers for DNS Management, and they will change the MX record etc. to point at their services: 

This means that you have to use their Public website too, so if you have a website hosted on that domain already, you might just want to change the MX Records:

rrmdesignAuthor Commented:

Thank you for the links, however, we are comfortable with DNS settings, we are mainly wondering that since we are planning on running a hybrid environment if we change our MX records will mail still flow to our on-premise Exchange server.

James HodgeManaging DirectorCommented:
Hi Nepal,

You will need to setup a shared address space.

Check out the info under 'Hybrid Email Routing':

A little more info on the subject:

Vasil Michev (MVP)Commented:
The MX does NOT need to point to Exchange Online, that's the whole idea behind hybrid. In fact, it can point wherever - on prem, the cloud, even third party scanning service/smarthost.

Just verify the domain intent in the Admin Center or using PowerShell:


And when you do a mailbox move, you need to use the service domain ( as the Target Delivery Domain

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