MTA may refer to a Mail Transfer Agent, a Message Transfer Agent, or a Mail Transport Agent. No matter which name you use, MTAs play an essential role in the Internet message handling system. They transfer electronic mail messages between the computers of a sender and a recipient.
An MTA is just an element of the email delivery process. It receives an email from the mail/message submission agent (MSA), which, in turn, receives it from the mail user agent (MUA). The MUA is commonly known as an email client – an app you use to handle email-related stuff.