Short for message transfer agent, MTA is the program responsible for receiving incoming emails and delivering the messages to individual users. The MTA transfers messages between computers.
How MTA Works
Hidden from the average user, the message transfer agent is responsible for routing messages to their proper destinations. MTAs receive messages from both MUAs and other MTAs, although single-user machines more often retrieve mail messages using POP.
The MTA is commonly referred to as the mail server program. UNIX sendmail and Microsoft Exchange Sever are two examples of MTAs.