The "Blacklist" section allows you to define a list of email addresses you do not wish to receive emails from. When first accessing this page, there are no email addresses in the list.
In Standard WebMail's email list, you can use the "Block sender" button to add an address to the blacklist.
Manage existing blacklisted addresses
If you entered an email address by accident or you do not wish to block it anymore, click its corresponding delete button.
Adding new address to blacklist
To add an address to the "Blacklist", type it in the "Email:" text field and click the "Add" button.
More options for the "Blacklist" functionality are available in the Ajax WebMail interface. Use the "Blacklist" in the Ajax WebMail if you want to add wildcards to substitute a part of the email address (e.g. *@example.com).