When speaking to another member in your inbox, you can easily see if they've read your message and they can see if you have read theirs. This will help your conversations flow more smoothly. 

On the website:

Once you have sent a message and the other member has read it, an eye icon will pop up underneath the message that says 'Seen by' 

On the app:

When you send a message, the word 'Sent' will pop up on the bottom right corner of the message  

Once the other member has read it, the message will change to 'Seen'