Mail Transfer Agent
A mail transfer agent or message transfer agent ( MTA ) is the software of a mail server that receives and sends e-mails . In contrast, the Mail User Agent (MUA) is used to process mails by the computer user . In multi-user systems , a mail delivery agent can also be used as an alternative to the MTA .
MTAs very often communicate according to the Simple Mail Transfer Protocol , but also according to X.400 . The recipient's MTA works with the mail server's Mail Delivery Agent (MDA), which delivers the e-mails to the appropriate mailboxes in the respective user directories . The Local Mail Transfer Protocol can be used for this. If a mail server is designed as an SMTP relay , it can also consist of just one MTA.
An integral part of an MTA is its queue . There he collects orders, especially if the MTA of the addressee (recipient) cannot be reached immediately. In this case, he goes through the addressee's MX resource records several times in order to process the order. If this fails, it sends a message back to the sender that the email could not be delivered (see also Delivery Status Notification ).
The MTA is the part of a mail server that is most vulnerable to computer security , e.g. B. through the intrusion of malware . It is also the email server component that offers measures to prevent spam .