Microsoft shares fix for Outlook login errors in Exchange environments

Microsoft has shared a fix for Outlook sign-in errors that iOS and Android users may encounter with mailboxes in some Exchange environments.

Affected users will see "<user email address> has been blocked on this device by your administrator" error messages.

"The error occurs in a hybrid Exchange environment, for mailboxes in on-premises Microsoft Exchange Server or Exchange Online," the company said in a support document released on Tuesday.

According to Redmond, the likely cause is a missing Exchange ActiveSync (EAS) access rule that would allow users using Outlook iOS and Android apps to connect to the Exchange Online server.

To resolve these connectivity problems, admins must ensure that hybrid Modern Auth is toggled on and add a new Exchange Online access rule for mobile Outlook apps.

The procedure required to that requires them to:

Verify that you've enabled support for hybrid Modern authentication in your organization (more information is available in this support document) Create an EAS device access rule in Exchange Online that allows connections from Outlook for iOS and Android. To do this, run the following commands: Connect-ExchangeOnline New-ActiveSyncDeviceAccessRule -Characteristic DeviceModel -QueryString "Outlook for iOS and Android" -AccessLevel Allow

Last year, Microsoft also provided a workaround for a separate and ongoing known issue causing sign-in issues for some Outlook for Microsoft 365 customers and blocking them from accessing their accounts.

This issue only impacts users who sign into Outlook using their Outlook.com accounts or those who have already added the accounts to their Outlook profiles. 

Until a fix is available, Redmond recommends toggling off Support Diagnostics, which would address the root cause of these login problems.

"To work around the issue, you can turn off Support Diagnostics, which turns off the option to submit an In App ticket using Help and then selecting Contact Support," Microsoft said in October.

"The bug is related to how Outlook is authenticating for the diagnostics in some situations."

The company also rolled out a fix for another issue known since August that was causing Outlook for Microsoft 365 to freeze and crash after launch.