This is where I say I will license a royalty-free license to my essential patents, and in return I expect you to license your essential patents to me on an royalty-free basis.
Microsoft's directory of intellectual property
we will license this to you royalty free
What is the worst thing MS can reasonably do?
But lets not waste our time on this discussion on the mailing list, forlegal matters, you should get legal counsel. Have your lawyers engage Microsoft on this topic, that is the only way of getting a solid answer.