Re-creating some of Hey's features using Fastmail
nunodonato.com
nunodonato.com
Yes, you can do that in Fastly, but it's a cludge. You have to maintain contact groups, which means that every new sort "rule" involves a contact add plus a visit to the contacts page to put them in the right group. There's nothing stopping Fastly from making this dead simple, but it's not dead simple right now.
And on top of that, there are benefits to building a UI around Hey's rigid bucket structure. The "feed" area, for example, shows the first few hundred pixels of every email just like it's a feed reader. You get the cool "focus and reply" screen for emails you've put off.
I think, if you really like Hey, use Hey, don't try to recreate it somewhere else. If you're on Fastly, you probably already have a really good system that works great for you, so stick with that.