You need one license of Address Magic (either Personal or Enterprise) for each mailbox that you plan to convert. A single mailbox may have multiple address books. This means, for example, that if one person has both a laptop and a desktop computer, you need only one license. Similarly, if you transfer addresses from an old computer to a new computer, it's only one mailbox and you need one license. However, if one computer is shared by two separate people, you need two licenses for Address Magic, even if a single person actually runs Address Magic to convert both address books.