This guide details the Libraesva ESG License Accounting system, focusing on the two primary licensing models: the Email Address accounting model and the Mailbox accounting model. The Email Address model accounts for active recipient addresses based on successfully sent or received emails, excluding invalid addresses. Recipients remain accounted for until they expire after 30 days of inactivity or are invalidated. The Mailbox accounting model identifies actively used mailboxes based on user management information. It typically results in a lower license count by excluding distribution lists and secondary emails. The document also explains the new 'Functional User' type introduced in ESG 5.2, which does not count towards mailbox licensing. Additionally, it outlines the licensing knowledge base, including different license types and their implications. The guide emphasizes the importance of proper user management and periodic maintenance to ensure accurate license accounting, especially when integrating with external systems like Microsoft 365 and Google Workspace.