Subject: Re: mail to
To: None <>
From: Thomas Mueller <>
List: netbsd-users
Date: 02/14/2001 03:26:02
>i can't reply to your mail:
>Feb 12 07:13:36 wojtek sendmail[3229]: f1ADXVm03046: to=<>, 
>ctladdr=<> (1000/100), delay=1+16:39:48, xdelay=00:00:23, 
>mailer=esmtp, pri=5190677, [], 
>dsn=4.3.0, stat=Deferred: 
>451 Open relay output - see
>i'm not relaying through so don't understand

ORBS has a database of open mail relays that some ISPs use to keep out spam.
Maybe your mail server is not configured properly, so outside users can send
email through that server?  Remedy is for the administrators to correct the
software so that outside users are barred from sending email through the server.