Alias from another domain with O365

Copper Contributor



I will try to explain my question without any errors:


The company that im working bought 2 O365 subscription ( we bought another company in the meantime). They used one O365 subscription for the main company and the other for the new company.


This was the first mistake they made, since they could add the 2 domains under one tennant, if i´m not mistaken. 



We want that the users from the first company to have an alias from the second company. From what i have been digging, that isn´t possible, since these are two driferent tennants.


The solutions i found imply create the domain from tennant b in the main tennant, so that the users can have that alias.

This won´t work since the doamin is already in use in another O365.Am I wrong? 


Question 2:


If i invite useres using the Microsoft Entra( Azure), they can acess all the apps? If i have a shared calendar in Tennnat A can the users i invited from tennant B work with it?


I could do a migration, but i thnk i need to buy more licenses on tennant A to acomodate the users from Tennnat B ( and add the domain in tennant A) Once again I´m i Wrong?


9 Replies
Yes, a domain can only exist in a single tenant. Microsoft did preview a functionality that allows "sharing" the domain, but that's still not generally available, afaik. You can however use a subdomain, if that fits your needs.
Guest access allows access to most, but not all workloads. Exchange for example does not support guest access, though if you are only interested in calendar sharing, this can be achieved natively via org relationships:
If you decide to go with migration, Microsoft should be able to assist with transferring the licenses.

@Vasil Michev 


Thank you for your reply Vasil.


one doubt arised with your awnser. When you wrote " You can however use a subdomain, if that fits your needs.", what are you implying? How does that Work? 





For question1, yes, Domain is in separate unless subscript another Domain and attach to your tenant

For question2, it is possible by establish integration such as cross-cloud B2B, btw, seems migration is between for your situation

If you have added in tenant A, you can add in another tenant, and any additional subdomains as needed.

@Vasil Michev 


Thank you for your reply.


I did a test with another domain i have: 


I add a new domain in the main tennant. Gave an alias to my account.


When i open my outlook ( desktop Version), i can use the Alias for sending and receiving. The issue i found is that the recciver will see the name only from my main domain and not from the Alias i sent.


Example email address removed for privacy reasons ( main account) email address removed for privacy reasons is the Alias. 


Sending e-mail from email address removed for privacy reasons is received has email address removed for privacy reasons


I have checked on exchange online for enabling Mailflow. 


What am i missing here? Or is it impossible for the name to appear?

Exchange always uses the default (primary) email alias for sending. If you want to send via additional alias, you need to enable this first:
Greetings Vasil,

We did some more attempts:

1) When sending an e-mail we can choose from wich alias we sen. It works fine if we send for mailboxes outside the company, since the Alias will appear correctly.

2) If we send from Alias to another tennant inside the company the name that will show will be the main domain.

When we reply to an e-mail received from the Alias, it will always send from the primary e-mail. We have to change manually to the Alias.

At this point the only question we have is for the reply not using the e-mail Alias from wich was received.

Any thoughts in how to solve this

Best regards.


The behavior will depend on the client I guess. I have no trouble with this in Gmail - when I hit reply, it composes a message to the "alias" address. Keep in mind that internally, Outlook will "resolve" the alias to the user name instead.
Once again thank you for your reply.

This discussion can be closed. After some digging and browsing the info from microsoft, this beaviour is indeed something that one could expect from using Exchange. Works fine the sent to and recieve, but when replying it will use always the default profile/name. To change the reply for the alias we have to do it on manual.