Mullvad and CounterMail allegedly do a good job of this (retaining no user data). However, USA authorities occasionally look into what it would take, in a legal sense, to force companies to write and distribute edited code to gain more access to customer data that the company immediately lacks[0]. For now it’s probably a bridge too far for law enforcement agencies, but one can never be sure about the future.

0: https://archive.is/jd7LT