E-mail is transitioning to web based central/closed services. For example in Sweden - government do not send e-mail, instead they use a private proprietary service that require an Android or iPhone for second factor access, as an alternative to snail mail.

So if you want to keep messaging decentralized, open and standardized, instead of just complaining, we need to try out things like e-mail signing. In order to improve we need to feel the pain points and engineer them away.