The point of this story is that open source can't protect you against a bully with a legal department at his command, and neither can it protect you against bad contract clauses. Frivolous legal threats may be frivolous, but you have to prove that in court and a lot of companies would rather take the easier way out to avoid having to do that.

The "FOSS" company never directly threatened the author, but the implication of it alone was enough to scare off both agencies. Given a lot of the tech is mixed up here on purpose, there's a few FOSS companies & vendors I can think of with legal departments that I'd describe as "pretty aggressive" and "expensive for a managed solution" that aren't solely about Exchange related services but would definitely behave like this, given their PR over the years at times has had slipped masks.