Thank you in advance for your response.
I am implementing a feature of messages for a web app.
The main idea of the business is that I have customers and suppliers. So, the first ones are able to contact the suppliers to ask them questions about the service they provide.
Then, both suppliers and customers have an 'inbox' view in which they can browse through the different threads of conversations and select one to read it's messages, just like with an email client.
Unread messages are marked differently in the inbox (with a lighter color) and there is also an indicator at the top navbar that shows how many unread messages you have.
So far so good.
When a new message is created, an email to it's addressee is sent. Users are able to reply to the message directly on the app or replying to the email.
Hence my question: Should I mark messages as read if an user replied to it by email?
Clearly, the message that is being replied has been read, but what about the previous ones? Should all be marked as read? Or would it be confusing for the user? And what about if I don't mark any of the messages as read? The next time the user logs in into the app he will see a notification saying that he has unread messages, but they may already have been read and even replied to.
Tank you again for sharing your opinions and wisdom.