This is a desktop mail client. It is also a web-mail you can run on a server somewhere if you so choose. It depends on how it is deployed. Contrasting Mailpile

This is a desktop mail client. It is also a web-mail you can run on a server somewhere if you so choose. It depends on how it is deployed. Contrasting Mailpile with other tools, one difference is that the basic design is that of a search engine, not a tool for reading mail from folders. Most current desktop mail clients are built on top of a bad paradigm, in my opinion. Another exciting thing about this model, is that since the UI is a website (of sorts), we can leverage the collective experience and creativity of the web design community. That is a much, much larger pool of talent than UI designers who know C++ or Objective C, or whatever. Finally, making the app a web server means you get an API to interact with your e-mail almost for free.