If you're an email power user the default iOS mail app probably isn't good enough for you.
We've tested a few mail apps for iOS and have come to the conclusion that Spark by Readdle is the best mail app if you have multiple email accounts.
One of the great features about Spark is that it works across the iPhone, iPad and Apple Watch so everything stays in sync.
If you've ever used or seen Inbox by Gmail you'll have noticed their very awesome sorting of emails into different categories. Spark has that functionality and can do it for any email account, it doesn't have to be Gmail.
If you're into swipe gestures you'll be pleased to know that Spark has a lot of useful ones. You can swipe left or right on emails to reveal various options.