While #Gmail and #Proton is currently the most trusted of all communication apps based on their past records, @skiffprivacy ,@Dmailofficial@cryptpad are not doing bad with their development in few years,they are Innovations that have credible usecases and possible adoption
@skiffprivacy is a privacy first end to end encrypted and open source collaboration mail with massive development going on the project .
Here are some of the #usecases, limitations and possible adoption level I can spot ,there are may be more