All Mail is your archive, a storage place for all the mail you've ever sent or received, but have not deleted.
You can see a list of archived messages by clicking All Mail. Archived messages are also available by searching, and under any assigned labels.
To archive mail:
- Select the message(s) you'd like to archive by checking the box(es) next to the sender's name.
- Click Archive at the top of your inbox.
You also can archive mail after you open it -- just click Archive along the top of the message.