The plugin spec allows for user authentication--But it seems to be in process.

Due to current UI limitations, we are not allowing plugins with User authentication into the plugin store. We expect this to change in the near future.

For now if you get development access you can run it on localhost and just make it available to yourself. So something early access could be a GitHub download and make your own copy for yourself kind of thing.

ETA: I do like the idea of some email integration. Assuming one is fine with ChatGPT knowing your email contents.