[pmmail-list] HELO - Not...Re: Another new beta 2627 posted

[L.Willms]

On Wed, 04 Sep 2002 22:50:24 -0400, Rich wrote:

> HELO being the same from two different accounts on the same computer is the 
whole point. 
> Not only do I have a half dozen different 'domains' that I send/receive 
from, but I work for a 
> company from here (as opposed to 'there'). When I send an e-mail from that 
company account, 
> it would be better for the e-mail to reflect that. 

   You are mixing up SMTP (RFC 2821), the mail transport, with its Mail 
Transfer Agents, and the MAIL document, with its authors, originators, 
senders, recipients, etc. 

   With HELO (today better: EHLO), an SMTP client identifies itself as a Mail 
Transfer Agent, not the sender or even less the author of a message being 
transported. The domain it identifies itself with is the domain of the MTA's 
host, not the one of the senders mailbox. Both can be different. On SMTP 
level, the sender's address is mentionend in the MAIL FROM command. 

   RFC 2821 (the current version replacing RFC 821) says the following about 
the host and domain, as being used in EHLO: 

--------- cut --------------------

2.3.4 Host

   For the purposes of this specification, a host is a computer system
   attached to the Internet (or, in some cases, to a private TCP/IP
   network) and supporting the SMTP protocol.  Hosts are known by names
   (see "domain"); identifying them by numerical address is discouraged.

2.3.5 Domain

   A domain (or domain name) consists of one or more dot-separated
   components.  These components ("labels" in DNS terminology [22]) are
   restricted for SMTP purposes to consist of a sequence of letters,
   digits, and hyphens drawn from the ASCII character set [1].  Domain
   names are used as names of hosts and of other entities in the domain
   name hierarchy.  For example, a domain may refer to an alias (label
   of a CNAME RR) or the label of Mail eXchanger records to be used to
   deliver mail instead of representing a host name.  See [22] and
   section 5 of this specification.

   The domain name, as described in this document and in [22], is the
   entire, fully-qualified name (often referred to as an "FQDN").  A
   domain name that is not in FQDN form is no more than a local alias.
   Local aliases MUST NOT appear in any SMTP transaction.

----- cut off ----------------

   Well, the letter rule is not practical, in my opinion, for all the private 
PCs and SOHO networks which link to the Internet via a dial-up connection and 
which do not have names assigned in the domain name system. The IP address, 
which I have given my PC in my local net, which is given as an alternative in 
section 3.6 of RFC 2821 is not a sensible alternative, in my humble opinion. 

   But anyway, If the SMTP client would read the sender's address and use the 
domain part of that as the domain in the EHLO command, this would result quite 
confusing e.g. in the case of the several million clients of T-Online which 
would all identify themselves as "EHLO t-online.de", and this vis à vis the 
T-Online mail servers. Can't make sense, right? 

    Find RFCs at http://www.rfc-editor.org/

Yours, 
Lüko Willms
-----------------------------------------------
Frankfurt/Main  

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