Add another Domain to our Office 365 tenant

Copper Contributor

Hello all,

We have a tenant which is recently we bought a new company and we want to add their domain into our tenant so we can assign license E1 and E3 for the users on domain

Does this configuration will work without interfering with our actual email from our tenant (

Can you provide step-by-step to do so?

At the end we want users from to be part of our tenant for us it will be much easier to manage with only one tenant!


Thank you for your precious collaboration!


Best regards,

5 Replies

Hi @SilverStar 


Provided you own the domain, you can add additional domains to your M365 tenant without interrupting existing domains.


The above shows you how. One thing to note is that if is already set up as a domain in another M365 tenant, then it must be removed before you can add it to yours. 


Good morning HidMov...

Thank you I already consult this article from know my main concern if I add the domain will I be able to add DNS records (MX records) so the newly domain can send and received email without causing any issue for our main domain which is

Domain are not in Microsoft 365 yet...this is why I am asking the question to incorporate this domain into our existing tenant some people say this:

  • No it is not as easy as adding an SMTP domain and you have a couple options available
    • Full maintenance of separate tenants
    • A migration of one tenant to another and set up a “send as” group email rule

You can add the SMTP and receive emails for domain 2 , but NOT send as


Best regards HidMov and have a nice day!

best response confirmed by SilverStar (Copper Contributor)

Hi @SilverStar 


For your main concern - adding in and pointing the MX records to your 365 tenant will not have any impact to your domain - it is entirely separate. Your existing users can have a alias if you wish, but it will not change their primary smtp/upn. 


You need to ensure you have a plan for the email migration for into your O365 tenant. What is servicing the email at the moment - hosted email, Gmail, Exchange on prem etc - and how will you migrate users to the new domain? Are there on-prem Active Directories?



Hello @HidMov 


HidMov -thank you so much for those clarifications it's very appreciated.

Actually, they are no plan for users from domain we will not migrate their actual email, we will start from scratch and import .pst file into their Outlook at the end. We simply want them to have a central repository for their emails...our Microsoft 365 tenant will do this.

So at the end our plan is to:

1-add domain into our tenant

2-configure DNS stuff on our tenant for domain

3-create users form domain into our tenant

4-assign license to them...Am I missing something?


Best regards,



Hi @SilverStar 


I'd personally make the DNS changes one of the last things to do. If you make the MX changes before the mailboxes in O365 have been provisioned, then any email sent to would be rejected until the mailboxes are ready to receive them which would be a pretty big disruption.


1. add domain to the tenant

2. Create users in the tenant

3. Assign licences

4. change MX/autodiscover/SPF records to point to M365

5. You may need to recreate Outlook profiles for users


Depending on how much legacy email and the tolerance level users will have to not having their email, I would look to import the bulk of the psts between point 3 and 4, and do another sweep after point 4 in case any emails have been delivered to the old mail server.


Hope this helps,