Folks I am using sendmail as my mail server. SELINUX is disabled. I observe messages in Centos 7 (and 6) in /var/log/messages, similar to: saslauthd[2765]: do_auth : auth failure: [user=bettie] [service=smtp] [realm=] [mech=pam] [reason=PAM auth error] I guess that this is because somebody tried to access one of the SMTP ports with a logon attempt. This is understandable; there are crackers out there. I'd like to block SMTP completely from the originating sender (by dropping the IP packets), but don't know how to figure out what the IP address is. I don't see anything in the "maillog" that, for example, has the name "bettie" or some other clue. The only thing I see is a message like sendmail[5452]: v9HIoBox005452: [xxx.xxx.xxx.xxx] did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA with a close timestamp, but I'm reluctant to tie the two log entries together. Is there some log, or log setting that might enable me to tie the do_auth error to a specific IP address? I'm very reluctant to change mail servers to postfix or something like that. Thanks David