Sync Public Folders to Exchange online fails Unable to create a remote shell session to Exchange Online. The error is as follows: "Connecting to remote server outlook.office365.com failed with the following error message : Access is denied.

Question

I am performing an Exchange 2013 to Office365 Migration. I am at the point where I need to make on-prem public folders visible to Office365 mailboxes. I am attempting to run the script sync-modernmailpublicfolders.ps1 per guidance provided here: https://learn.microsoft.com/en-us/exchange/hybrid-deployment/set-up-modern-hybrid-public-folders. Running the script returns:
InitializeExchangeOnlineRemoteSession : Unable to create a remote shell session to Exchange Online. The error is as
follows: "Connecting to remote server outlook.office365.com failed with the following error message : Access is
denied. For more information, see the about_Remote_Troubleshooting Help topic.".
At C:\script\Sync-ModernMailPublicFolders.ps1:506 char:5

• InitializeExchangeOnlineRemoteSession;
• ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
• CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
• FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,InitializeExchangeOnlineRemoteSession

The account being used is has the Office 365 Global Administrator and Exchange Online Organization Management roles assigned. The account does not require MFA. In the same powershell session I can "connect-ExchangeOnline" without issue, so I'm thinking the error message may be misleading or bogus. I've run this script many times in the past in other organizations and never had a problem. On-Prem Exchange 2013 CU23 is patched to within thirty days. I have run the script on different Exchange servers, always with the same result. I have tried running the script in the EMS and in Windows Powershell. All powershell on Exchange servers reports same powershell version:
PS C:\script> $psversiontable

Name Value

---

PSVersion 5.1.14409.1018
PSEdition Desktop
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0...}
BuildVersion 10.0.14409.1018
CLRVersion 4.0.30319.42000
WSManStackVersion 3.0
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1

I have opened a support call with Microsoft, but am not getting anywhere. I'm hoping someone out there has run into this one.

TIA
Tom

Answer 1

I'm thinking it has to do with not supporting Modern Authentication and "I THINK" that Microsoft is starting to phase out basic authentication. I need to test this myself but here's a discussion on github that talks about it and a potential workaround.

https://github.com/MicrosoftDocs/OfficeDocs-Exchange/issues/1563

Answer 2

I too am having this issue.
Exchange 2016 setup with Hybrid Simple Configuration with Office 365
I was able to migrate a test mailbox to Office 365 from on-premises. Once that was done the O365 mailbox cannot access the Public Folders on-site.
Until we can get this fixed we cannot migrate to Office 365 fully.
I had Conditional Access requiring MFA for all users but I made an exception for my account. My account has full admin access to Office 365.
I verified that the account did not have MFA "Enforced" on the individual account
The Azure Security defaults are off
Under the "Modern Authentication" section of Settings>Org Settings, I had "Allow access to basic authentication protocols" unchecked for Exchange Online PowerShell originally but then checked it so that it will allow access and it still does not work. Maybe I have to wait for that setting to apply?
Regardless, I can try tomorrow but below is the output I get too.

[PS] C:\pfscripts>.\Sync-ModernMailPublicFolders.ps1 -Credential (Get-Credential) -CsvSummaryFile:c:\pfscripts\sync_summ


cmdlet Get-Credential at command pipeline position 1
Supply values for the following parameters:
Credential
[10/7/2021 2:46:19 PM] Creating an Exchange Online remote session...
InitializeExchangeOnlineRemoteSession : Unable to create a remote shell session to Exchange Online. The error is as
follows: "Connecting to remote server outlook.office365.com failed with the following error message : Access is
denied. For more information, see the about_Remote_Troubleshooting Help topic.".
At C:\pfscripts\Sync-ModernMailPublicFolders.ps1:506 char:5
+     InitializeExchangeOnlineRemoteSession;
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Write-Error], WriteErrorException
    + FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,InitializeExchangeOnlineRemoteSession

Answer 3

Anyone ever get this to work? I am facing the same issue.