No reputable email service will allow you to use it to commit crimes. If the activity is against their ToS, and they get a legal warrant to provide information to the authorities, then this goes beyond any reasonable expectation of privacy.
Mailfence is pretty open about this[1]. Their privacy policy[2] also seems reasonable. Their only obligation is complying with Belgian law, and I'll take that any day over a service within the Five Eyes jurisdiction.
[1]: https://blog.mailfence.com/transparency-report-and-warrant-c...