VSys One comes with a list of e-mail domains that it "knows" are bogus: ".cmo", "gmaill.com", "gmal.com", etc. These are usually common typos for manually entered e-mail addresses. From the Letters/e-mails panel, click on E-mail known bad domains. Here you can edit the existing domains or add new ones of your own.
Whenever you enter an e-mail address into VSys One that ends in one of these values, VSys will highlight it in orange, indicating that it's probably typed in wrong!