Two companies one tenant, advice welcome


Hi All,


I'm trying to decide the best way to handle the following scenario, any input would be greatly appreciated.


So a small business has a few users typically the business owner and an admin person and perhaps some general staff but runs two similar companies that have different names & domains, say company A deals with one market segment and company B deals with another but are similar. The staff's roles are typically the same for both businesses.  The way I see it you would have to add both domains to O365 and decide on which business will be the primary, the business owner and admin person need mailboxes for both domains so do you add an Exchange Plan 1 licence to these users (say they have Business Premium or Microsoft 365 Business for the primary company) or would you use a shared mailbox to achieve this?


I guess what I'm asking is there a sure fire way to handle these types of company setups or is it always going to get messy?


I deal with a lot of smaller (5-20 user) companies and this type of multi-company setup is becoming more common.

7 Replies
You're right - I've dealt with a few of these myself and they are generally somewhat messy.
Skype meeting and OneDrive URLs are generated by the domain, so in theory external users shouldn't ever see the wrong brand unless logos show up in Skype meting invites on in the banner for Yammer or files.

Thanks for the feedback @Loryan Strant , I guess I'm just trying to come up with a SOP for these types of setup.


For staff that need a mailbox on both domains would you configure a shared mailbox for the second domain or do you add an additional Exchange Online Plan 1 licence to their existing Microsoft 365 / Office 365 Business Premium (if that's even possible)?


I think it’s always going to be a little messy too.  For the mailboxes, if it didn’t matter what the sending domain was, you can always set up the second company as an alias on the primary mailbox.  The downside is that you can’t send from an alias, so any outgoing emails would always come from company 1.


I think if you have to be able to send from both company 1 and company 2, I would go with your method of just creating a second users for company 2 and then purchasing an Exchange only license for them.  In effect I have this in my tenant only it’s a primary account for my company and a secondary account (with an exchange only licenses) for one of my personal email address/domains.  Since they are in the same tenant, you can open the secondary mailbox from within OWA (while signed into the first) if you set up all the permissions correctly, or you just sent up both accounts in Outlook on the desktop (or mobile).


Just my two cents, but I think you have a couple different ways you could do it without any one choice being inherintly better, they all have various advantages/disadvantes.


In fact you can send as alias using ChooseFrom 365 cloud service, especially if you prefer to run a single mailbox for 2 companies. 

A way I've done this in the past is based on this -

Basically, User1 mailbox has address only

Create a DL, with address

Add User 1 to DL

Grant User 1 'Send As' rights on DL

emails to and end up in User1 mailbox

When sending, User1 needs to use the 'From' field in Outlook, entering the DL name, if wanting to send from address, or leave blank if sending from address.

Alternatively you can use ChooseFrom 365 cloud service.

It looks like you cannot create a DL using if 'user' is being used as a username for a user. This 'user' can be used as an alias of the same user with ability to receive mail sent to either or
Sending mail 'as' doesn't work on me. (Mail is sent but 'send as' or 'on behalf of' is stripped off and only is left in the sender field)