We have customers that do not allow App Registrations to be created for Multiple Tenants, but the current email integration uses the "common" endpoint thus requiring the App registration to be multi tenant.

I cannot see any reason or use cases where it makes sense that this App Registration is multi tenant, since you cannot add users to BC from another tenant AFAIK

I guess it can be fairly easily changed, by using the tenant specific endpoint in this:

procedure GetAzureADAuthEndpoint() AuthEndpoint: Text

  var

    NavUserAccountHelper: DotNet NavUserAccountHelper;

  begin

    AuthEndpoint := NavUserAccountHelper.GetTokenAuthorityEndpointServerSetting();

    if AuthEndpoint = '' then begin

      Session.LogMessage('0000GN6', NoServerAuthEndpointTelemetryErr, Verbosity::Warning, DataClassification::SystemMetadata, TelemetryScope::ExtensionPublisher, 'Category', TelemetryCategoryLbl);

      if IsPPE() then

        AuthEndpoint := 'https://login.windows-ppe.net/'

      else

        AuthEndpoint := 'https://login.microsoftonline.com/';

    end;

    exit(DelChr(AuthEndpoint, '>', '/') + '/common/oauth2/authorize');

  end;

Change common to the tenant id please. Alternatively make it a setting

br

Michael