My aix boxes have the port 25 listening and I want to bock that. But before that I want to check the recent logs of the sendmail activity and any open sockets using the port. Please advise.
Well, don't launch sendmail -bd, the usual mail server app. You can block a listening port with some mechanisms, like firewall SW jammed in the stack beside the NICs.
netstat -a will show any connections, but mail is a short connection protocol, like http/1.0 not persistent. lsof will tell you about every open fd on the system, including sockets. Sendmail logs somewhere, check the man page, config files.