Need Help Figuring Out Domain Sharing Solution

Regular Visitor

I have two groups of an organization who are REQUIRED to have separate Microsoft 365 tenants.  Please do not suggest combining them, as that is not a solution for my query.


However, they do want to have the same outward facing email domain.  I know that I can't split spf, so therefore I cannot add the same domain to both Microsoft 365 accounts.  So my thought was to route all email through the main "primary" tenant.  


However, how can I provide users on the separate tenant the ability to send under the primary domain name?  Is the only way to do this to configure their outlook clients with accounts on the main domain to allow them to send as on the mail client and have them sign into everything else with their separate tenant account?  Is there another way to configure mail routing so that users sending from the Outlook web app will be able to send as that domain name?  Any suggestions would be helpful.

2 Replies

Hey @microworker 


See if the address rewriting service using exchange server meets your requirements:


If you are looking for paid solutions Quest does provide a coexistence service, you might have to give them a call to discuss your situation where you will not be migrating the users would rather stick with coexistence mode: