Subject: smtpupd-09 prohibits firewalls and home networks

From: "D. J. Bernstein" <[email-masked]>
Date: 29 Jan 1999 20:43:44 -0000

> Only resolvable, fully-qualified, domain names (FQDNs) are permitted when
> domain names are used in SMTP.

This requirement prohibits the behavior of many existing clients, as I
explained in June 1998.

It means, for example, that a client relaying a message to a smarthost
is violating the protocol if the user typed an address incorrectly.

To obey this requirement, the client has to check every address in DNS.
This is an unacceptable policy violation at some corporate sites, an
unacceptable expense for many dumb clients, and an unacceptable obstacle
for the vast majority of users when their ISPs are temporarily unable to
reach the rest of the Internet.

Fix: Remove ``resolvable.''

(The above requirement also prohibits all use of domain literals. There
is a subsequent exception for EHLO, but what about the standard use of
domain literals as specified in RFC 1123? I don't recall any discussion
of this on DRUMS; I don't know if it's anything more than a huge mistake
by the document editor.)

---Dan