Stopping messages without To: or Cc: header(s)

[Hugo van der Kooij]

On 22/11/09 10:02, Glenn Steen wrote:
> Is there explicit support for this type of rejection in the standard?
> I thought it only implied...;-)
> Many distribution list thingies use this, not only baddies. I suppose
> you've analysed it a bit already...?

Well. RFC5322 does not make them required.

    +----------------+--------+------------+----------------------------+
    | Field          | Min    | Max number | Notes                      |
    |                | number |            |                            |
    +----------------+--------+------------+----------------------------+
    | trace          | 0      | unlimited  | Block prepended - see      |
    |                |        |            | 3.6.7                      |
    | resent-date    | 0*     | unlimited* | One per block, required if |
    |                |        |            | other resent fields are    |
    |                |        |            | present - see 3.6.6        |
    | resent-from    | 0      | unlimited* | One per block - see 3.6.6  |
    | resent-sender  | 0*     | unlimited* | One per block, MUST occur  |
    |                |        |            | with multi-address         |
    |                |        |            | resent-from - see 3.6.6    |
    | resent-to      | 0      | unlimited* | One per block - see 3.6.6  |
    | resent-cc      | 0      | unlimited* | One per block - see 3.6.6  |
    | resent-bcc     | 0      | unlimited* | One per block - see 3.6.6  |
    | resent-msg-id  | 0      | unlimited* | One per block - see 3.6.6  |
    | orig-date      | 1      | 1          |                            |
    | from           | 1      | 1          | See sender and 3.6.2       |
    | sender         | 0*     | 1          | MUST occur with            |
    |                |        |            | multi-address from - see   |
    |                |        |            | 3.6.2                      |
    | reply-to       | 0      | 1          |                            |
    | to             | 0      | 1          |                            |
    | cc             | 0      | 1          |                            |
    | bcc            | 0      | 1          |                            |
    | message-id     | 0*     | 1          | SHOULD be present - see    |
    |                |        |            | 3.6.4                      |
    | in-reply-to    | 0*     | 1          | SHOULD occur in some       |
    |                |        |            | replies - see 3.6.4        |
    | references     | 0*     | 1          | SHOULD occur in some       |
    |                |        |            | replies - see 3.6.4        |
    | subject        | 0      | 1          |                            |
    | comments       | 0      | unlimited  |                            |
    | keywords       | 0      | unlimited  |                            |
    | optional-field | 0      | unlimited  |                            |
    +----------------+--------+------------+----------------------------+

But in my experience all newsletters I am expecting and all mailinglists 
I have subscribed to make proper use of at least the To: or Cc: header.

Hugo.