Mail Delivery Agent
A Mail Delivery Agent ( MDA) is a software for the delivery of e -mails to the user accounts in question.
Mail Delivery Agents in addition to mail user agents, the two original components of systems for e-mail. Because each mail user agent can access only to a single user directory, a mail delivery agent is tasked with the delivery, which is equipped by the root account with elevated privileges.
With the client - server model, Mail Transfer Agents and the Simple Mail Transfer Protocol were added. In addition to this network protocol Mail Delivery Agents can use the Local Mail Transfer Protocol.
Independent implementations of Mail Delivery Agents are also called simply mail filter: