Other people already mentioned Roundcube and Snappymail, which are good options already.

There’s also Cypht if you want a different approach. It combines multiple accounts into same interface so you can have a unified inbox.

That’s interesting, I’m using it since android 4 days, don’t remember a single crash. If that’s the only case it crashes, I would open an issue and use it in the meanwhile. Check the permissions maybe?

Binaryeye supports both decoding and encoding via Share menu. So you can share an image from any app to decode(can also be a photo that has a qr code somewhere). It also supports sharing a text or link to generate one. It also has searchable history support.