We are not aware of other FOSS development teams that have as extensive knowledge, both theoretical and practical, about #email and #openpgp and regularly release across all platforms for users world wide ... except for #protonmail with whose technical and security experts we discuss regularly. They are the other major game in town doing pervasive email encryption after all. Did you know that Proton's and delta's VCards are compatible across ecosystems and establish immediate encryption?

@alandes in delta you can "attach" contact and then save or share the resulting file. On protons side maybe this helps https://proton.me/support/adding-contacts