IDT, Inc. Lightweight MTA Authentication Protocol (LMAP) is the general term for a family of proposed protocols to help address the spam problem by permitting domains to publish the set of SMTP clients which may use their name in the EHLO/HELO and MAIL FROM fields. SMTP servers can use this information to determine if a client is consensually using a domains name. This document discusses the applicability, and the costs and benefits of wide-spread deployment of the protocol family.