IMAP, with enhancements like: 1. threaded email conversations supported natively 2. folders treated as gmail-like labels (essentially, tags) 3. advanced sear

IMAP, with enhancements like: 1. threaded email conversations supported natively 2. folders treated as gmail-like labels (essentially, tags) 3. advanced search and saved search queries supported natively Also, an implementation better than Gmail's which does not have arbitrary limits on bandwidth/data used and number of connections.