It is not possible to look up your email password but you can change it to anything you want.
Log in to your control panel. Start by logging into our CLIENT AREA. Then click on My Services, then click the Square green icon to the right of your domain. Click the Logon to Plesk button.
Click on the Mail tab.
Click on the email address for which you want to set the password.
Type in the new password and click OK. Write down the password as you will need to put it in your email program.