!

exim.conf
....
hostlist   local_net = 127.0.0.1 : 192.168.0.0/16
....
acl_smtp_rcpt = acl_check_rcpt
....
acl_check_rcpt:
  drop   hosts           = !+local_net
         local_parts     = ^root
         log_message     = Mail to root from inside

- .
Exim . . . , postfix.
!