Fortinet FortiMail 3.0 MR4 - Manual (Page 337)

set system opmode
FortiMail™ Secure Messaging Platform Version 3.0 MR4 CLI Reference
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system opmode
Use this command to change the operation mode (opmode) of the FortiMail unit.
Only the default FortiMail system administrator account can change the opmode of the FortiMail unit.
You will need to login again after changing the opmode.
Changing the opmode between gateway and server modes will result in all settings being changed to
factory defaults except the configuration for the port1 interface
Changing the opmode to or from transparent mode will result in all settings being changed back to
factory defaults.
Syntax
set system opmode {gateway | server | transparent}
History
Note: It is recommended that you back up the FortiMail configuration before changing the opmode.
FortiMail v3.0 New.