I set up Let's Encrypt for an older Exchange server a while ago. While I love the result, it was NOT a simple, one-line exercise.

Up to date documentation was near-impossible to find, and the scripts that came out of the box on the recommended client needed some fixing. The whole thing took about half a day, plus some hours a few weeks later once the unforgiving anti-abuse thresholds I accidentally triggered during end-to-end testing finally expired. Definitely wasn't a pleasant experience.