dear sockpuppet =) I think the above commenter meant illegal physical access. The jabber.ru MitM situation was likely carried out by a cybercrime unit of the German police forces with a court order... and this is the adversary most people forget about.

Lesson to learn: Let's Encrypt does not protect against MitM by a state-level actor, unless you take precautions. *let's assume network admins won't MitM your server for personal vengeance reasons