A Mail Transfer Agent (MTA) is a software application that facilitates the sending and receiving 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 accurately. When an email is sent, the MTA checks the recipient's address and determines the best route for delivery. If the recipient's server is unavailable, the MTA can store the message temporarily and attempt to resend it later. This ensures reliable communication over the internet.