Microsoft has issued a fix for sign-in errors that iOS and Android users might face with some Exchange mailboxes. The error message will read “<user email address> has been blocked on this device by your administrator.”
The problem happens in a hybrid Exchange environment for mailboxes in on-premises Microsoft Exchange Server or Exchange Online, Microsoft said in a support document released on Tuesday.
To fix the issue, administrators must enable support for hybrid Modern authentication and add a new Exchange Online access rule for mobile Outlook apps.
Microsoft has also previously provided a workaround for a different ongoing issue causing sign-in problems for some Outlook for Microsoft 365 customers, which only impacts users who sign into Outlook using their Outlook.com accounts or those who have already added the accounts to their Outlook profiles.
Redmond suggests turning off Support Diagnostics until a fix is available. The company has also rolled out a fix for another issue known since August that caused Outlook for Microsoft 365 to freeze and crash after launch.
To resolve the connectivity problems in this case, admins must create an EAS device access rule in Exchange Online that allows connections from Outlook for iOS and Android.
The company said the most likely cause is a missing Exchange ActiveSync (EAS) access rule, which would enable users using Outlook iOS and Android apps to connect to the Exchange Online server.
The procedure required for that involves verifying that hybrid Modern authentication support is enabled and running specific commands to create the EAS device access rule in Exchange Online.
Microsoft has issued a fix for the Outlook sign-in errors that iOS and Android users might face with some Exchange mailboxes. Affected users will receive “<user email address> has been blocked on this device by your administrator” error messages.
To fix the issue, administrators must ensure that hybrid Modern authentication is enabled and add a new Exchange Online access rule for mobile Outlook apps.
