How to reset the password for an email address you have set up in your Plesk control panel
1. Login to Plesk control panel.
2. Click on Subscriptions in the left hand pane and then select the subscription containing the mail account.
3. Click the Mail tab.
4. Then click on the email account you would like to change the password on.
5. Enter a new password into the password fields or click the Generate button to get Plesk to generate a password for you.
6. Click OK