What I like about Hey:
- Screener feature that let's you just quickly hide senders (or whole sender domains) quickly
- The three basic categories, Imbox, Feed and Papertrail work great for me. I never used folders or labels in Fastmail or Gmail, but I use this categorization
- The Recycling feature that automatically deletes old emails is a nice touch
On top of that Hey for Work offers great collab features like sharing an email thread with a coworker without needing to do the BCC dance (they get instant access to the whole thread), thread merging and thread collections are also useful features (not exclusive to Hey for Work, but I found them most useful in a work context).
Their customer support is also super fast and helpful.
Some comments here mention that it feel slow and sluggish. For me it's as fast as Fastmail, faster than the bloated Gmail for sure.
I was using Fastmail before and also liked it - but what sets Hey apart from Fastmail is that they are trying new things to improve the whole email experience. I understand that it might not work for some people, but it sure works for me.