Here's some advice from Linux guru Bryan Lunduke

https://lunduke.substack.com/p/down-the-rabbit-hole-making-my-life?utm_source=post-email-title&publication_id=462466&post_id=75643846&isFreemail=false&utm_medium=email

To get to the gist he uses KolabNow for email but cites ProtonMail as an option.