[Mimedefang] Testing HELO

[David F. Skoll]

On Tue, 14 Oct 2003, Les Mikesell wrote:

> There is not a 1 to 1 correspondence between hosts and IP numbers
> and I'm pretty sure sendmail does not go out if it's way to
> care about which interface it is using for each connection.

Sending a raw IP address violates RFC 2821, and in my book, that's
a good enough reason to reject the connection.  From the RFC:

   -  The domain name given in the EHLO command MUST BE either a primary
      host name (a domain name that resolves to an A RR) or, if the host
      has no name, an address literal as described in section 4.1.1.1.

So:

	EHLO roaringpenguin.com
	EHLO [216.191.236.23]

are both OK, but:

	EHLO 216.191.236.23

is *not*.  Any SMTP client that issues a EHLO command followed by
a raw IPv4 address not inside square brackets is in violation of RFC 2821.
I suppose a host that uses HELO rather than EHLO may have been in existence
prior to RFC 2821, but unfortunately, the Milter API makes no distinction
between HELO and EHLO.

Regards,

David.