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hs_nico's avatar
hs_nico
Copper Contributor
Apr 03, 2024
Solved

Access mailbox as an external user

How can a user from Tenant A access their mailbox in Tenant B?

 

My current situation:

  • I have set up B2B collaboration in Microsoft Entra External ID
  • I invited a user from Tenant A to Tenant B
  • This user is of type member (not guest)
  • This user has the identity ExternalAzureAD
  • In Tenant A the user has the Microsoft 365 Business Premium license
  • In Tenant B the user has the Exchange Online (Plan 1) license
  • There is a mailbox for the user in Tenant B
    • Other users from TenantB can access it
    • The emails from this mailbox can be forwarded
  • In Tenant B the user can be added as a member of a shared mailbox

But how can the user access these mailboxes? When I try to add a new account in Outlook and enter the user principal name (Tenant B) I get the following error code: CONNECTFAILED. When I select "Open another mailbox" in Outlook on the web and enter the userprincipal name there, I get this error:
BootResult: accessDenied
err: Microsoft.Exchange.Data.Storage.MailboxUnavailableException
et: ServerError
estack: Microsoft.Mapi.MapiExceptionUnknownUser

 

Feels like I'm almost there. I “just” have to log in. :smile:

 

Thank you very much for your help and kind regards
Nico

Authentication
Azure Active Directory (AAD)
Azure AD B2B

3 Replies

    • hs_nico's avatar
      hs_nico
      Copper Contributor
      Apr 04, 2024

      VasilMichev, thank you for your quick reply. :smile:

       

      It's a shame that doesn't work. Why can I create a mailbox for the external user and give this user access to shared mailboxes if he can't use them at all?

       

      Do you have any idea if this will be supported at some point?
      Since the topic of multitenant organizations is still very new in Microsoft 365, I hope that this scenario will be supported at some point. Not much is missing anymore, just the login. :lol:

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