To get started you'll first create the email accounts through your control panel at 'wcp.hostek.com'. Once that is done, you'll log into the Webmail for one of the users (by clicking the Webmail icon next to the email address in the control panel).

Once inside the user's Webmail you'll go into the Settings section, then expand the My Settings folder. Next, expand the Advanced Settings subfolder and click the Mailbox Migration button to get started.

This will launch a popup window that asks what type of server you're migrating from. Here you'll choose "Other" then click "Next". Now you'll check the box for "Email" and click "Next". Now you should see a screen that asks for the connection info for the other server. Select IMAP as the "Type", then enter the rest of the connection details. Once you click the "Next" button the emails will be imported for that account.

Repeat that process for the rest of your domain's email accounts.