SMTP? Never heard of it. This library is more for developing chrome extensions that take advantage of gmail's DOM and UI state

This API is for interacting with Gmail's user interface more so than for interacting with its back-end data.

AFAIK Gmail's implementation of IMAP is kind of borked and stuff like the "smart" categorization (e.g. social networks, notifications, etc) doesn't reflect into imap folders (or RSS their RSS feeds, for that matter). Labels do, though, with a workaround.