Addresses are kept in the form of templates called patterns both in black and white lists.
A valid pattern can be formatted as <site> or <e-mail>@<site>, where <site> is a series of labels glued with '.' (dot) characters. The allowed formats for the site part are ASCII and IDN.
You can use an asterisk (*) as a substitute for a number of letters, and question mark (?) as a substitute for a single letter. For example: firstname.lastname@example.org, email@example.com, *@spammers.net. Specifying *@spammers.net will block the entire mail site spammers.net.