Just to talk about wording.
If I say to my (WhatsApp using) friends:
Heh, there is a new great Mail Client you can chat with.
They will answer: I don’t need a mail client. I use mail only very less. And I have a mail app which works good for me.
If I say there is a new great messenger you can reach everybody who have a mail address.
Hopfully they will install it side by side with WhatsApp.
Remember this is only my sight of this.
And belive me, in my milieu E-mail is really less important. Everybody does all via messengers.
I know, in Cuba E-mail is more popular then in many other countries.
Still I think a messenger should stay very plain in design.
Only the very important UI things and settings.
All my friends using for Mail on the mobile phone the special mail apps (f.g. for gmx they use the gmx app).
One time I tried to explain K9. Bad idea. There was to much settings. I like it but the “normal user”. will only use it without to have to much to configure.
The same for messengers.
The “normal user” want just start to chat.
Just a simple view of the current chats and a contact list.
You want another view for “normal” mails.
I’m sure that’s a bad idea.
A idea would be if someone would fork DC and integrate a mail view as you like.
This could exist side by side with DC. Maybe it will happens if DC and OX-Coi will be famous enough to be a replacement for WhatsApp.
Another mail client will never replace a messenger