Apple Mail.app hides Archive folder - how to get it to show
I just had this problem on OS 10.10 (Yosemite). Here's how I solved it:


Select the inbox.
Right-click "Account Info"
Select "Messages on Server" tab.
Wait until the size of all of your mailboxes is calculated.
Select the Archive mailbox and click "Show Messages" button.


The archive now appears in the mailboxes bar.