TypeApp marks emails as read or unread.
An empty circle is read, and a filled one designates an unread email. To further help to distinguish between read and unread, the sender and subject of an unread email will be bold. The color itself identifies the provider and helps you prioritize when using Unified Inbox so you can easily figure the account of that email.
To mark an email as read / unread swipe left on the email message and choose Mark Read /Mark Unread.
To enable or disable the unread indicator in TypeApp:
Tap More (o o o) | Global Settings | Customize Appearance | Design Preference | Read Indicator.