Hi-- I work at Nylas. Happy to jump in here :)<p>The sync engine handles all the compatibility or dozens of IMAP and Exchange servers, and uses a variety of heuristics for real-time notifications. It also does the heavy-lifting for the huge amount of data in most people&#x27;s mailbox. The N1 app can cache your entire archive in about 10% of the disk space required if you also download all unprocessed headers+attachments.<p>Right now our search implementation just sends a proxy request to the IMAP search, so you&#x27;ll get the same performance as Gmail web, Mac Mail, etc. It&#x27;s not ideal. We&#x27;re working on our own faster search system, but it&#x27;s tough to build a huge distributed search cluster that handles tens of terabytes. (And is growing quickly!) If anyone here wants to work on that, we&#x27;re also hiring. ;)<p>N1 is built on Electron, which under the hood is Chromium+NodeJS so that comes with a bit of weight. But the app itself is pretty manageable. You can check out the source here: <a href="https:&#x2F;&#x2F;github.com&#x2F;nylas&#x2F;n1" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;nylas&#x2F;n1</a>