‘This XML file does not appear to have any style information associated with it’ error in MailStore when logging in using Modern Authentication

When users attempt to login to MailStore Using Microsoft login credentials, after authenticating directly with Microsoft they are redirected to a Mailstore URL and receive the following error:

This is due to there being no ID token being passed back from Microsoft Azure AD after the user authenticates. This is typically due to a setting being missed in Azure AD app registration and the following should be checked:

  1. Open the Azure Portal at https://portal.azure.com/
  2. Select Azure Active Directory.
  3. Select App registrations under the Manage list.
  4. Under All Applications select the MailStore Application you previously configured.
  5. Select the link under the Redirect URIs section.
  6. Scroll down and confirm ID tokens (used for implicit and hybrid flows) is enabled.
  7. Save the changes and retry the login steps.