If you are using sendmail under an RHEL derivative, the sendmail.mc file needs to be edited. CAUTION: be sure to deny relay for any network that you NOT on.
dnl # The following causes sendmail to only listen on the IPv4 loopback address
127.0.0.1 and not on any other network devices. Remove the loopback
dnl # address restriction to accept email from the internet or intranet.
dnl DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl
Insert 'dnl' in front of 127.0.0.1
In the access file, place your local network where 192.168.1.0 is
# by default we allow relaying from localhost...
You will need to restart sendmail to compile the access.db