I think most people these days have switched to webmail in one form or another. Build this as a web app, not a strict desktop client.
The demo has it running on OSX. OSX users are more open to the idea of having (and paying for) a desktop application. From a business perspective, an OSX desktop application might make sense.
The demo has it running on OSX. OSX users are more open to the idea of having (and paying for) a desktop application. From a business perspective, an OSX desktop application might make sense.