Question : Sendmail Open Relay

We have sendmail 8.11.6 server running on RH 7.3 with internal ip 192.168.123.89.  Our MX record points to public ip of xxx.xxx.xxx.xxx, however we have a SGS 5420 (Symantec Gateway Security) which performs address redirection from the public ip of xxx.xxx.xxx.xxx to 192.168.123.89.  Currently the sendmail server appears to open relay.  I'm not sure why sendmail is open relay but I believe this is because sendmail thinks all email is coming from 192.168.123.1 (internal IP of symantec gateway).  In the access database, we have a rule to relay for 192.168.123 as we obviously want to relay for internal clients.  Any ideas greatly appreciated.

Answer : Sendmail Open Relay

What you really want here is to allow all clients inside of the firewall relay privs except the IP of the mail gateway. I see that I had the IP of that wrong in my earlier comment (the gateway is 192.168.123.1). So your access map needs to look like:

localhost.localdomain   RELAY
localhost   RELAY
127.0.0.1   RELAY
192.168.123.2  RELAY
192.168.123.3  RELAY
192.168.123.4  RELAY
192.168.123.5  RELAY
192.168.123.6  RELAY
192.168.123.7  RELAY
...
192.168.123.254  RELAY