[geeks] A puzzling mail error

[Rich Kulawiec]

On Tue, Jun 24, 2008 at 07:16:36PM -0400, Phil Stracchino wrote:
> That's when this started happening:
> 
> Jun 24 19:04:56 babylon5 postfix/smtpd[27566]: NOQUEUE: reject: RCPT
> from pond.babcom.com[10.24.32.25]: 553 5.7.1 <[127.0.0.1]>: Helo command
> rejected: mail server in loopback network (test);
> from=<goose at caerllewys.net> to=<alaric at caerllewys.net> proto=ESMTP
> helo=<[127.0.0.1]>
> 
> I like the way it asserts that 10.24.32.35 is 127.0.0.1.  Or is it
> trying to tell me that pond (.35) just suddenly started claiming to be
> loopback in its HELO?  It seems kinda surprising a release would have
> gotten out the door if it did something that blatant.

I believe it's trying to tell you that pond is HELOing as [127.0.0.1].
It's permissible for a host to HELO as a bracketed dotted-quad, e.g.

	HELO [1.2.3.4]

or a FQDN

	HELO mail.example.com

so that's syntactically valid, but it's not semantically valid because
it'd shouldn't HELO as the loopback address (or as the receiving mail
server, which is a form of brokeness seen from some spambots).  Thus
postfix is giving you "Helo command rejected" 'cause it knows that's bogus.

(Aside: "HELO 1.2.3.4" is broken: missing brackets.  "HELO mail" is
broken: not a FQDN.  "HELO fubar.example.com" is broken if
fubar.example.com does not exist in DNS.  "HELO [192.168.0.1]" is broken
if received on an external interface that shouldn't be talking to
anything in RFC 1918 space.  And so on.)

---Rsk