I switched back to Airmail on OS X last week as it was pretty obvious Mailbox was dead as there were 2 critical bugs regarding switch and images not loading that hadn't been fixed in months. It's a shame but that's life.

I have to manually setup the rules/filters for now but reading through some other clients in the app store they seem to be buggy. I used Airmail years ago before Mailbox and it was stable and has been since switching back.

I went from Sparrow to Mailbox to Airmail. Sparrow was the best for its time. Mailbox had potential but was riddled with bugs. Airmail doesn't have the cleanest interface nor all the coolest features, but it's the best option I've found at the moment. For iOS I am still using Mailbox, but I guess now I have to use something else, will probably give the Gmail client a go.

One OSX client I've just found that I'm hoping does what I need: https://nylas.com/N1 It's open source.

The AirMail UI needs work but I use it for its support of Markdown - one of the areas that really needs polishing.

Check out Spark by Readdle. It replaces Mailbox fairly well.

Agreed! It had great functionality, including customizabiltit and the best approach to separating wheat from chaff I've seen to date. Spark is entirely client side (Though they're hinting at adding server-side features; as long as it doesn't include server-side access to my email no problem).

Mac client slated for early 2016. They support plain IMAP (yes!) and even Exchange.

Spark and Outlook seem to be the most delightful to use.

I'm quite happy with Spark, been using it the last few months. I got tired of Gmail's webapp app.

i think we're better of going for a paid email client instead of depending on these free ones.. that get acquired and shut down

For what it's worth, Sparrow was a paid client (~$10) with a free version that had ads and limited functionality.