Randy Grimshaw writes :
> You can add the following rule to the *check_mail* hook in sendmail
> R$*<> $#error $@ 5.7.1 $: "551 You must provide a proper from address"
Please be very careful when doing this type of thing. A blank envelope sender
is used to identify an undeliverable mail notification. See rfc821
This notification message must be from the server-SMTP at this
host. Of course, server-SMTPs should not send notification
messages about problems with notification messages. One way to
prevent loops in error reporting is to specify a null reverse-path
in the MAIL command of a notification message. When such a
message is relayed it is permissible to leave the reverse-path
null. A MAIL command with a null reverse-path appears as follows:
Breaking messages from Mailer Daemons may cause you problems more serious
> This will require the sender to provide something as a mail from: value
> and then any content given will be checked by the regular tests that you
> provide. See sendmail.org for additional info about the hook.
> <><Randall Grimshaw, Network Programmer, Syracuse University, 315-443-5779
> On Fri, 6 Mar 1998, Chris Brenton wrote:
> > The blank return path bothered me. I've tested this off of a few mail systems
> > and was surprised to see that all of them would accept a blank "mail from:"
> > line. Are there any firewalls out there that would kick this message out by
> > default? Mail systems?