The first thing you need to do is hit the Windows button to switch to the Start Screen, then launch the Mail app.
Now move your mouse to the bottom right hand corner of your screen, which will bring up the Charms Bar. Then click on the Settings Charm.
Now open Accounts under Settings.
Then click on the Add an Account button.
Now choose the Other account option.
Next, choose the IMAP option.
Now you will need to enter you email address and your password, then click on the Show more details link.
Now, enter your IMAP and SMTP server settings provided in the email Smarsh sent to you.
Once you finish entering the server information, your mailbox should be set up and ready to go.