Hey does not support IMAP and that's its most important feature
blog.vrypan.net
1 thread
Paid email without IMAP is like renting a house and you're not given the keys.
And now that I think of it. IMAP (more or less) allows you to download your mbox file. Why downloading using HTTP is so much worst (it isn't) than using IMAP?
email was working long before there was IMAP. If you want your "keys", you have to be able to download your mbox file (which is possible in hey).