Problem with e-mail server

Hello,

I have a problem when the mail server is connected through the FortiGate 60E.

FortiGate local IP is detected instead of client local IP each time when a user is trying to connect to his email address and this thing is causing server blocking FortiGate local IP , in case of a Brute Force attack, instead of blocking individual client IP.

Is there a way to forward client IP to the email server ?

Thank you

Kind regards.