Messageware NavGuard (NG) issue after applying M2.1 mitigation update

This article applies to the following products:

·         Messageware NavGuard 2019

·         Messageware NavGuard 2016

Summary

After applying the Microsoft M2.1 mitigation, a blank window is displayed after logging on to OWA.

This issue is caused by a compatibility issue between M2.1 and Messageware NavGuard’s navigation security controls.

Solution

Microsoft documents a two-step approach to removing M2.1 mitigation, after applying the June 2026 security updates.

If mitigation was applied using Exchange Emergency Mitigation (EM) Service:

1. Block the mitigation M2.1.0 from re-applying. 
2. Remove the mitigation M2 IIS rules.

If mitigation was applied using the downloadable EOMT script https://aka.ms/UnifiedEOMT:

1. Roll back the mitigation.