I've been using Boxer. After many fits and starts over the years, it's actually become a pretty good email app. I like it a lot better than Outlook on Android and I prefer it to the gMail app. I remember that the Verge gave it an honorable mention on iOS (not sure about Android).
The Android Premium version's also basically free -- you just have to email/SMS 10 people with free Premium codes to get Premium yourself. It's USD9.99 otherwise. Exchange access is a 9.99IAP separate from Premium. I was one of the early Beta testers of the app so I got Exchange free on my One M8 in addition to Premium -- but I've changed phones 6 times since then so I lost it.
Anyway, if you don't want to spam your contacts just get the delivery number of a bunch of pizza (or whatever) shops and temporarily save those to your contacts -- the app doesn't distinguish between terrestrial and cellular numbers so once you've 'sent' an SMS to those numbers, you're golden. If I recall correctly, you don't even need to actually send the message -- I had my Note5 on airplane mode (with Wi-Fi on) when I did this (I forgot why I was) and it still gave me the unlock code even though I never actually sent anything to anyone.
Also, join the Google+ community for Beta access. Those are usually stable enough for use as daily drivers and you get fixes/new features quicker. They update around once or twice a week.