LFCS: Linux Foundation Certified System AdministratorDemo

A Mail Transfer Agent (MTA) is software that transfers email messages between servers using protocols such as SMTP. Postfix, Sendmail, and Exim are all well-established, widely deployed MTA software packages used on Unix/Linux systems to route and deliver email across networks. Procmail, in contrast, is a Mail Delivery Agent (MDA) used for local mail filtering and sorting after delivery, not for transferring mail between hosts, so it does not qualify as an MTA. "SMTPd" is not a standard standalone MTA product name recognized in this context.