After trying to open a mailbox on Outlook, the following error is generated: Cannot expand the folder. The set of folders cannot be opened. Microsoft Exchange is not available. Either there are network problems or the Exchange server is down for maintenance.
On Event Viwer the following error was generated:
Cannot expand the folder. The set of folders cannot be opened. Microsoft Exchange is not available. Either there are network problems or the Exchange server is down for maintenance.
Using the Fiddler to get more conclusive logs about the error, I noticed that Autodiscover was running successfully, the SOAP response was bringing the right data from the mailbox without any issues. Thereafter the SSL handshake was also running successfully.
However, after Autodiscover and SSL Handshake was concluded, Outlook should start the connections to open the mailbox in RPC over HTTP or MAPI over HTTP, but the connection doesn’t happen. I parsed the logs and got the following error:
Microsoft.Exchange.Rpc.RpcException: Client is being backed off —> Microsoft.Exchange.RpcClientAccess.ServerTooBusyException: Client is being backed off —> Microsoft.Exchange.RpcClientAccess.ClientBackoffException: Client connect is backed off —> Microsoft.Exchange.RpcClientAccess.Server.LoginPermException: ‘User SID: S-1-5-21-1144410367-3042246465-1959246801-1157’ can’t act as owner of a UserMailbox object ‘/o=First Organization/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=f55dcba97d594669b25c157afdc26b40-Linke’ with SID S-1-5-21-1144410367-3042246465-1959246801-1156 and MasterAccountSid (StoreError=LoginPerm)
at Microsoft.Exchange.RpcClientAccess.Server.UserManager.User.CorrelateIdentityWithLegacyDN(ClientSecurityContext clientSecurityContext)
at Microsoft.Exchange.RpcClientAccess.Server.RpcDispatch.ExecuteWrapper(Func`1 getExecuteParameters, Func`1 executeDelegate, Action`1 exceptionSerializationDelegate)
As we can see a user with SID “X” cannot open the mailbox with the SID “Y” because it is not allowed to do so. The error was clearly as if I were trying to open a mailbox using a user I did not have permission to do. However, the scenario was not this. I was trying to open the mailbox of user “Y” using the credentials of user Y, so this error made no sense at all.
To try to fix the error, I tried to open using the login in netBIOS (contoso\user) and UPN (user@contoso) format. In both modes the error was always the same.
Checking which was the SID that corresponding to user “X”, I validated that it corresponded to a user named l7. But the user that I was trying to open the mailbox was user l6.
With a little research, I confirmed that the problem is related with credentials. Perhaps the reason is some bug which makes Windows not applying the credentials that I typed to login on Exchange. Instead of applying the credentials which I typed, Windows used the credentials of user l7 that were saved in “Windows Credentials”. This is because l7 already had an Outlook profile configured on the computer.
I deleted all credentials linked to those names used by Exchange (mail and autodiscover).
After the removal of those credentials, I was able to open the mailbox without issues.