> It's kind of a pity you can't just do a 'sendmail -send-only' and have
> it just sit there processing the queue as needed, and have it refuse in-
> coming connections (if, as you say, everything gets routed through the
> mail hubs, and all the aliases and translations are set correctly).  If
> configured correctly, this would permit the client to send mail outward
> and not require it to listen for incoming mail (since even if it were
> to bounce back, the mail hub would properly re-route it).

'sendmail -q30m' does this. All our clients except the mailhub do this,
and a "telnet client smtp" gets "connection refused."