I am working on a web-based email client (https://ronomon.com) with offline access, instant boot, constant time search, and support for roughly four million emails. It takes some new approaches to threading, meta-discussions, multiple sources, attachments, and simple non-structured text to-do lists, and re-imagines the email client as a multiplayer rather than single-player tool. Could I let you know when it's ready?
Please let me know when this is ready. My contact details are in my profile. I love trying to break stuff like this, and I've managed to break lots of webmail and email clients in the past.