A Mail Transfer Agent (MTA) is an SMTP server that relays email messages to another SMTP server.

FortiMail units operating in gateway mode function as an MTA. FortiMail units operating in server mode function as an MTA and full (SMTP, IMAP, POP3, webmail) email server.

In order to deliver email, unless the email is incoming and the email server has no domain name and is accessed by IP address only, MTAs must query a DNS server for the MX record and the corresponding A record. For more information, see “The role of DNS in email delivery”.