The Local Mail Transfer Protocol (LMTP) is a derivative of ESMTP, the extension of the Simple Mail Transfer Protocol (SMTP). It is defined in RFC 2033.

LMTP is designed as an alternative to normal SMTP for situations where the receiving side does not have a mail queue, such as a mail storage server acting as a Mail Delivery Agent (MDA). Mail queues are an inherent requisite of SMTP. In situations in which mail queues are not possible, LMTP is desirable, since a mail storage server should manage only its mail store without having to allocate more storage for a mail queue. This is not possible with SMTP when there are multiple recipients for a mail message. SMTP can only indicate successful delivery or failure for all or none of the recipients, creating the need for a separate queue to handle the failed recipients. LMTP, on the other hand, can indicate success or failure to the client for each recipient, allowing the client to handle the queueing instead. The client in this case would typically be an Internet-facing mail gateway. LMTP is not intended for use over wide area networks. In other words, the Message transfer agent (MTA) still handles all outgoing mail, including the mail stream from the LMTP, to another mail server located somewhere on the Internet.