1. Log into the Customer Control Panel with your main account's username and password.
2. Under the "Home" tab, you'll see the "Plesk" section at the bottom of the page, click on "Login via IP address".
3. Once logged into the "Plesk" you'll see "My Webspaces", click on the "Manage Hosting" link.
4. You'll see the domain or domains you want to manage, under each domain you'll see tabs, click on the "Mail" tab for the domain you want to manage.
5. You'll see the list of the email accounts for that specific domain.
6. There you can add a new email account or manage the existing accounts you have.