If you want to verify that you know your email password, you can easily verify it using the webmail interface.
Webmail login location:
If your domain name is domain.com, then your webmail login would be at: http://www.domain.com/roundcube If you can successfully log in there, then you know that you have the right email username and password.
If you have forgotten your email password, you will have to set a new password in the hosting control panel.
The login location for your hosting control panel is your website address with ":2222" appended to the end of it. So using the example above, if your domain is domain.com, your hosting control panel address is at http://www.domain.com:2222