Zimbra Mail Transfer Agent The Zimbra MTA (Mail Transfer Agent) receives mail via SMTP and routes each message using Local Mail Transfer Protocol (LMTP) to the appropriate Zimbra mailbox server. The Zimbra MTA server includes the following programs: Postfix MTA for mail routing, mail relay, and attachment blocking. Clam AntiVirus for scanning email messages and attachments in email messages for viruses. SpamAssassin to identify unsolicited commercial email (spam). Amavisd-New used as an interface between Postfix and ClamAV / SpamAssassin. Milter servers to filter email ReciptTo content for alias domains and to filter restricted sender addresses for distribution lists. In the VMware Zimbra Collaboration Server configuration, mail transfer and delivery are distinct functions. Postfix primarily acts as a MTA, and the Zimbra mail server acts as a Mail Delivery Agent (MDA). The MTA configuration is stored in LDAP. A configuration script polls the LDAP directory every two minutes for modifications and updates the Postfix configuration files with the changes.
