Users prompted for credentials after adding a shared mailbox as a second Exchange email account in their Outlook profile

Applies to: Exchange OnlineExchange Server 2016 Enterprise EditionExchange Server 2016 Standard Edition


Consider the following scenario:

  • You have a hybrid deployment of on-premises Microsoft Exchange Server and Microsoft Exchange Online in Office 365.
  • You configured legacy on-premises public folders for a hybrid deployment.
  • You create a shared mailbox that's located in Exchange Online.
  • You assign Full Access permissions to one or more users.
  • Users add shared mailboxes as second Exchange accounts in their existing Outlook profile.
In this scenario, users are repeatedly prompted for credentials when they open Outlook.


To work around the problem, move the shared mailbox to the on-premises environment.


Outlook tries to connect to the legacy public folders for the shared mailbox account. An error message that resembles the following is found in the RPC Client Access service log for this connection attempt:
[LoginPermException] 'User SID: S-1-5-21-1458817636-171340609-1824194506-1199' can't act as owner of a MailUser 
object '/o=ExchangeLabs/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=189bd14f1ede49d7977
85e8f20d55edf-Shared Mail' with SID S-1-5-21-1458817636-171340609-1824194506-1207 and MasterAccountSid S-1-5-10
For more information, see Configure legacy on-premises public folders for a hybrid deployment.

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