your phone will start ringing that a few of your clients have to wait 30secs at least to send a mail
well, as helo, i'm using deny if no hello was used
and i'm not checking the helo parameters, that's just pointless
and again, i would only check hello for unathenticated users, because i'm not playing with my clients, it's against spammers
and AUTH is after HELO
so it gets complicated
wanna check my config as an example?