Office365 B2B Exchange mailboxes

  • Goal: Have a user from one Azure AD tenant be able to have and login to their own exchange online mailbox (not just getting forwarded email) on another Azure AD tenant using their own original credentials.

    So far I've tried adding a guest user, convert the account to a member and assign a licence. That creates a mailbox for them that another user can get delegated access to, but there doesn't seem to be a way for that user to access the mailbox using their credentials. The portal let me reset the password for the account. (AAD portal did not because it recognizes it as an account from an external source) And then I could log in with that password.

    So at this point, it seems like the mailbox account created is separate from the actual Azure AD account, which leads me to believe that Exchange Online has no support for multitenant access.

    Is there some other way to meet this goal in Azure AD/Office365, or would the required solution be some kind of separate identity service?

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