Soverin is PGP encrypted the dutch www.bof.nl (bits of freedom) chose their service to provide secure e-mail
Tutanota is also available in a gratis option, but the space is then a bit limited.
I see how decentralised is better, but i have not found one yet that i would actually use.
I'll try to come back to this article to find more options.
Ok, thanks and good luck! :)