From - Fri Nov 30 16:34:25 2001
Date: Thu, 29 Nov 2001 19:53:16 -0800
To: Postfix users <postfix-users@postfix.org>
Subject: Re: Problem with Reply-To: and 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.

 sendmail just implements the standard. You may call that "stupid".