A Mail Transfer Agent (MTA) is software that facilitates the transfer of email messages between servers. It acts as a digital post office, routing emails from the sender's server to the recipient's server. MTAs use protocols like SMTP (Simple Mail Transfer Protocol) to ensure that messages are delivered efficiently and securely. MTAs can be standalone applications or part of a larger email system. They manage tasks such as queuing messages, retrying delivery if a server is unavailable, and handling errors. Popular examples of MTAs include Postfix, Sendmail, and Exim, each offering different features and configurations for email management.