When you whitelist an email address, it will bypass SpamExpert's mail filtering service. This is useful if, for example, a legitimate email has been blocked.
To do this, login to your control panel and select Virus and Spam Filtering from the top menu.
From the SpamExperts dashboard, select Sender whitelist.
You can add either a full email address, or whitelist a whole domain (e.g. by adding gmail.com). There is also the option to upload a CSV file if you have a large number of entries to add.