First, what device are you using? Phone, iPad or laptop?
If on a phone, you have to click the 3 bars upper right in the menu bar.
The envelope is always there in the menu bar at the top to access t-mail, it only turns red when you have new t-mail or reply. You can click on the gray envelope and you will see two options:
Access your full Tree-Mail Inbox
and
Compose a new mail.
Click that first one and you'll see your entire list of t-mails.