Mail fifth parameter

I have to send a email to a server where is very important the "Return-Path" to match the identity. If I use mail("user@example.com", "object", $message,"From: webmaster@domain.com\r\n". "Reply-To:webmaster@domain.com\r\n" ."Return-Path: webmaster@$domain.com\r\n); I see in the received message that return-path Is not that I want. I try to use the fifth parameter ( "-fwebmaster@domain.com) but I am in safe mode then I see the warning : the fifth parameter is disabled in safe mode. There is a workaround for this problem ? safe_mode = on is impossible for this server !