If you dig into the mail RFCs, you will note that the scope for “electronic mail” was a big vision of the future rather than the stuff it is used nowadays. Ever since http://quickmsg.vreeken.net/ showed off, I really liked the idea of “re-invisioning” mail as an messenger. Not because it solves all our problems, but because it solves the biggest one: adoption. Anyway, DeltaChat has finally reached a rather big milestone: For the first time they a serving both Android (F-Droid, as always, and now upcomming Play) and IOS builds as well as (some) desktop versions.
Don’t get me wrong, using mail is indeed a crude hack.. not only for messenger, but in general. But is actually used out there and it is not going away anytime soon. Leveraging this popularity is an outstanding move. Also: Autocrypt.