🚀 go-pugleaf

In article <929993490.18317.0.nnrp-03.d4e48b20@news.demon.co.uk>,
Alisdair Wren <alisdair@nospam.demon.co.uk> writes

>This may be slightly off-topic, but it is for messing around with IP 
>development.
>
>I was wondering about the specifics of the SMTP standards.

then you should look at the DRUMS drafts, which will change this area

>From RFC 1123:
>
>5.2.2  Canonicalization: RFC-821 Section 3.1
>       The domain names that a Sender-SMTP sends in MAIL and RCPT
>       commands MUST have been  "canonicalized," i.e., they must be
>       fully-qualified principal names or domain literals, not
>       nicknames or domain abbreviations.  A canonicalized name either
>       identifies a host directly or is an MX name; it cannot be a
>       CNAME.
>
>Now from this, it is implied that a setup like:
>
>   blah.foo.com         MX      smtpserver.foo.com
>   smtpserver.foo.com   CNAME   superserver.foo.com
>   superserver.foo.com  A       123.124.125.126
>
>Would be invalid,

it is certainly a bad idea -- mailers tend to look themselves up using
canonical names (look in the Cricket book!)

I don't think that SMTP specs can make DNS records invalid per se

> however, when I read it I see it to mean that in the 
>RCPT and MAIL lines, you can't have CNAMEs.

that is the current position

>  So:
>
>   MAIL TO:<user@blah.foo.com> is OK but,

from the DNS provided - yes, but if should be delivered to
123.124.125.126

>   MAIL TO:<user@smtpserver.foo.com> would not be.

it will work (see the caveat above) and will be legal soon(ish)

-- 
richard @ turnpike . com                         "Nothing seems the same
                          Still you never see the change from day to day
                                And no-one notices the customs slip away"