[brongondwana]

We're looking at making this easier, but you can already set up a separate login token for the individual SaaS products - just create a regular password alternative login with something from pwgen or your favourite line noise source.

https://www.fastmail.com/help/account/alternatelogin.html

You can then revoke the individual token.

Per-folder permissions isn't something on our radar yet. You could hack it up with a family/business and separate accounts with folder sharing, but it costs money and is a right pain to administrate.