I have been super frustrated with the stock email client on Android which seems to crash about 50% of the time when I reply to ActiveSync / Exchange email.
Last week I discovered Nine which handles both Exchange and GMail if you're an apps for business user. It handles email, calendar and tasks beautifully and can present a combined mailbox from several accounts. The app is nicely designed and so far hasn't crashed or hung for me which has reduced the amount of daily swearing I aim at my phone considerably.
If you need to access Exchange on Android I can't recommend Nine highly enough.
(Related: Is it safe to open securedoc.html (Cisco Registered Envelope)?; Sending email via GMail in C#/.NET using SmtpClient; Get an email when your security camera sees something new (Apps Script + Cloud Vision))