[Mailman-Users] Virtual hosts
brad at shub-internet.org
Wed Apr 11 05:55:13 CEST 2007
At 9:27 PM -0500 4/10/07, Brad Knowles wrote:
> The important sentence here is:
> | In the dot-atom form, this is interpreted as an Internet
> | domain name (either a host name or a mail exchanger name) as
> | described in [STD3, STD13, STD14].
> In particular, note that it says "host name" or "mail exchanger name",
> and specifically omits "CNAME alias", and refers you to STD3 (RFCs 1122
> and 1123) and STD13 (RFC 1034) for definitions of these terms.
In contrast, here's a quote from the cf/README file for sendmail 8.13.8:
| confDONT_EXPAND_CNAMES DontExpandCnames
| [False] If set, $[ ... $] lookups that
| do DNS based lookups do not expand
| CNAME records. This
| the published standards, but the IETF
| seems to be moving toward legalizing
| this. For example, if "FTP.Foo.ORG"
| is a CNAME for "Cruft.Foo.ORG", then
| with this option set a lookup of
| "FTP" will return "FTP.Foo.ORG"; if
| clear it returns
| you may not see any effect until your
| downstream neighbors stop doing CNAME
| lookups as well.
And the HISTORY file for postfix-2.4.1-RC1:
| Performance: RFC 2821 blesses the use of CNAME domain names
| in MAIL FROM and RCPT TO. Not having to expand CNAME domain
| names speeds things up a bit. File: smtp/smtp_proto.c.
Now, I'm still not seeing the part that Wietse is referring to. I'm
still checking the document.
However, Eric's comment in the sendmail cf/README file makes it plain
that this is a common behaviour that has been done for as long as
Internet e-mail has existed, and therefore it's going to be a very,
very long time before we can assume that most sites won't do this
kind of thing -- even if the IETF does finally codify the practice.
So, we're still going to need a FAQ on this subject, regardless of
whether the then-current RFCs require that CNAME aliases be resolved
to their actual canonical names or not.
Brad Knowles <brad at shub-internet.org>, Consultant & Author
LinkedIn Profile: <http://tinyurl.com/y8kpxu>
Slides from Invited Talks: <http://tinyurl.com/tj6q4>
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