About advertising type E-mail to people who established prior contact

A) Introduction

Several businesses engage in the practice of sending unsolicited E-mail
advertising their goods to people, with whom there was prior business
contact.

This practice is not always pleasurable for the recipients, but does not
quite fall into the definition of spam.

After a recent incident, to which Linux-IL subscribers witnessed, I have
the following idea about controlling this kind of E-mail.



B) The basic idea:

The companies in question often include at the end of the E-mail a
statement that the recipient is getting it because of prior contact and
that he can unsubscribe by sending a message to a certain E-mail
address.

My idea is to expect them to add to the statement also a dated
description of the prior contact in question.  For example "You attended
a course organized by us at 13.7.1978", or "You logged into our Web site
last time at 22.2.2002".

Then, any unsolicited commercial E-mail without such a statement can
automatically be considered as a spam.  Forged statements can be easily
caught, if the recipient has an archive on his PC.



C) Examples from sourceforge.net - could be improved:

1. Used in monthly mailings:
When the SF.net team sends out a site-wide email, we sometimes see
replies that look like this: "Hey! I didn't ask to be on this list! You
spammer. I hate you! I hate your dog! (insert other colorful phrases
here)." The truth is, when you registered on SourceForge.net there was a
check box that said "Receive Site-wide updates, low volume." You left it
checked when you submitted the registration form, hence you are
receiving this email. We send these updates every 4 to 6 weeks, so it
truly is low volume. However if you want off, this is not a problem.
Simply click on the link.

2. Used in a relatively recent E-mail:
This message was sent on behalf of SourceForge.net based on
the existence of your user account on our site.



D) Question:

Should a particular format be prescribed for such statements?
On one hand, any prescribed format is bound to be forged by spammers.
On the other hand, format will make it easier to parse and validate this
part of E-mail messages.  And we need the E-mail headers anyway to judge
whether it was sent by the bona fide sender or forged.

I'd like to know of any objections or refinements before I propose the
idea in its final form.
                                                --- Omer