[PATCH] sendmail: use host rather than NIS domain name for HELO

[Rich Felker]

On Fri, Apr 27, 2012 at 11:36:16AM +0100, Ron Yorston wrote:
> According to RFC 5321 the argument to HELO "contains the fully-qualified
> domain name of the SMTP client" or its IP address if no FQDN is available.
> BusyBox sendmail uses the NIS domain name instead which, in many cases,
> is likely to be the default "(none)".  Despite this BusyBox sendmail works
> because, per RFC 1123, the server "MUST NOT refuse to accept a message,
> even if the sender's HELO command fails verification".

My mailserver ignores this MUST, because ignoring it and rejecting
such behavior blocks 75-90% of spam before it even gets to the
filter/analysis stage, and doesn't block any mail from a *conformant*
sender.

I expect others might do the same, or at least add a very high spam
probability score to such broken senders. Thus, fixing busybox
sendmail in this regard should be considered important in my opinion.

Rich