Joining a bigger O365 without loosing administrative control

New Contributor


CompanyA  ( < 100 employee's) is bought by CompanyB (> 10k employee's).

CompanyA will keep its own AD and AAD (with AADC), and has a non-microsoft email solution.

Both want CompanyA to remain as agile as possible in their processes


CompanyB wants to integrate just the email environment in their O365 tenant, but CompanyA is afraid this will lead to massive delays in email account creation etcetera.

CompanyB is not a CSP, but

1) is there any (supported) solution that will give CompanyB admins to a (yet to be created) O365 tenant, prefferably housed in the current CompanyA AAD tenant?

2) or is it possible to have the companyA mx recoreds point to the companyB O365 where CompanyA can create mailboxes only for their domain (and given that the CompanyA AADC is not pointing to this tenant)?

(Given that both would be impossible, I would either setup custom scripting (via email) between the two tenants upon new user creation or give in and hand over the mx records to CompanyB.)

3 Replies

Addendum: The reason they want to integrate into the O365 environment is partly a wish from companyB, but mainly for the Cooperation capabilities. The other option for the latter would be inter-tenant collaboration

best response confirmed by KoenHalfwerk (New Contributor)

Since the end goal is to inevitably have all the users in the same tenant, it's best to just go with it. You can always assigns a limited role to the IT staff from Company A, with just enough rights to create mailboxes and perform whatever other tasks are necessary. It will be much easier/cheaper solution.


That said, there are some third-party products that can give you cross-tenant admin permissions, but of course they come at a price.

Thanks for the reply. I feared as much. I'll give it a go to try to convince CompanyB going CSP, but otherwise integration + some form of limited deligation seems to be a more elegant solution. Thanks!