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Re: Mandatory From field, anonymity, and hacks

2005-01-30 12:35:24

On Sat January 29 2005 04:23, Hector Santos wrote:

The first question.

Which software is responsible to make sure the format is correct?  The MUA?
The SMTP Receiver?

If that's a general question, the answer is a combination of
MUA and MSA (RFC 2476).
Most, if not all SMTP receivers detect valid headers and add what is

No, MTAs are not supposed to alter the message content except
to add trace fields (Received, Return-Path).  MSAs are permitted
to make specific modifications.
Based on RFC 822 (A.3.1.  Minimum required), a valid RFC 822 header is one
that has:

    Valid RFC header = Date: && From: && (cc: || bcc: || To:)

This was relaxed in RFC 2822 , where a valid RFC 2822 header is one that

    Valid RFC header = Date: && (From: || Sender: || Reply-To:)

RFC 2822 does not require a Sender field unless there are multiple
authors, and does not require Reply-To under any conditions.

Are you proposing further relaxation as follows?

822:    Valid RFC header = Date && (cc || bcc || To)
2822:   Valid RFC header = Date && (Sender || Reply-To)

See above and RFC 2822 section 3.6.

Yes, your error in interpretation of those RFC aside, the intention
is to make the From field optional. [MIME media type message/rfc822
has yet another set of rules, but a From field is not mandatory
there; however if a From field is absent, there must be at least
one of Subject or Date fields.]
From a point of view of Completeness:

Technically, a message needs no headers at all.

No, a message must have a message header, and that message
header must have at least one header field.  See RFC 822
section 4.1, RFC 2822 sections 3.5 & 3.6, and RFC 2046
section 5.2.1.

So the next and final question is:

Is a RFC header required in the DATA stage at all?

If that's an SMTP question, yes, because SMTP transfers
messages, and the message format (822/2822) requires a
header with certain fields.