After upgrading WorkgroupMail from WorkgroupMail v7 (or WorkgroupMail v6) to WorkgroupMail v8 the licence has changed to an evaluation licence.
This is intentional. When upgrading to WorkgroupMail v8 the existing licence is converted to a thirty day evaluation licence. During this period you must decide whether to purchase an upgrade to WorkgroupMail v8 to cover each of your licenced users. Click here to purchase.
Please refer to the following FAQ