FortiMail operation modes

FortiMail units can run in one of three operation modes: gateway mode, transparent mode, and server mode.

Gateway mode

• The FortiMail unit acts as a mail transfer agent (MTA), or email gateway, relaying email to and from the email servers that it protects.
• Simple DNS MX record change redirects email to FortiMail for antispam and antivirus scanning.
• FortiMail does not locally store email unless queued or quarantined.

Transparent mode

• The FortiMail unit transparently proxies or relays email traffic to and from the email servers that it protects.
• Eliminates the need to change existing mail server network configuration.
• FortiMail does not locally store email unless queued or quarantined.

Server mode

• The FortiMail unit operates as a standalone, full-featured email server and MTA.
• The FortiMail unit locally stores email for delivery to its email users. Email users can access their email using FortiMail webmail, POP3, or IMAP.

All operation modes can scan email traffic for viruses and spam, and can quarantine suspicious email and attachments.

Comparison of gateway, transparent, and server mode of operation

	Gateway	Transparent	Server
SMTP role	MTA/relay	Transparent proxy/relay	Server
FortiMail unit is hidden	No	Yes, if enabled	No
Email user accounts	Preferences and per-recipient quarantine only	Preferences and per-recipient quarantine only	Yes
Requires DNS record change	Yes	No, if hidden with no per-recipient quarantines or Bayesian scan	Yes
May require changes to SMTP client configurations or other infrastructure	Yes	No	Yes
Requires FortiMail unit located between external MTAs and protected email servers	No	Yes	N/A (FortiMail unit acts as email server)
Protected email servers	Separate	Separate	Integrated (FortiMail unit acts as email server)

In addition, some FortiMail features are specific to the operation mode. As a result, changing the operation mode may reset your FortiMail configuration.