In common with the majority of email users, I receive a considerable
amount of daily spam.  Most of the spam I receive has a remove html
tag on the bottom of the email which supposedly enables you to remove
yourself from a mailing list.  From what I have picked up generally it
is considered a no-no to click on one of these remove links and try
and remove yourself as the spammers then know that there is a 'live'
address - resulting in more spam.  However, I have yet to hear of any concrete
evidence other than the natural assumption that to reply to any of
these spammers would range from dumb to lunacy.  Perhaps I'm just too naive ;-)

My question is whether this is really true, and whether there are any
reports of people actually trying this out and getting removed, or
alternatively getting inundated as a result.  Although I do not think
for a second these spammers (porn/viagra/low mortgage
rates/health/diet etc.) have one reasonable bone in their bodies, I do
not want to just ignore the problem if in fact I might be able to
remove myself.

Dear dysan99, 

Yes, there is some numerical "proof" to the fact. My fellow Researcher
Read-2-Live once brought Phil Bradley's research to my attention.

Bradley wanted to check what the sources of spam are. He registered
himself with several email addresses, using in each another "spam
attracting" technique: using the opt-out options, joining or
participating in discussion groups, putting the address on a web page,
putting it on Hotmail's "White Pages".

The result is amazing. If the 8 different emails he grounded, the one
that "opted out" (and was never subscribed on the spam list on the
first place) got by far the most (Read Bradley's experiment at "The
Spam Experiment" <http://www.philb.com/spamex.htm>).

While Bradley's conclusions are not scientifically (you could always
claim that this case is particular to this opt-out list), it leaves in
my opinion little doubt n the affectivity of opt-outs.

The Centre for Democracy & Technology conducted a similar, more
controlled and more "scientific", experiment. Their findings are
different: they found that most of the spam arrives from addresses
advertised in public, and that most opt-out services respect this
request. However, their definition of an opt out service was different
than the one Bradley used: they signed to news services, and then
opted out - not tried to opt-out of spam they did not receive in the
first place (The Centre For Democracy & Technology, "Why Am I Getting
All This Spam? Unsolicited Commercial E-mail Research Six Month
Report" <http://www.cdt.org/speech/spam/030319spamreport.shtml>).

However, there are some supportive evidences that it is not that
dangerous. Matt Lake of CNet performed a similar experiment. He
claims, that most spam opt-out links *that were not broken or crooked
in some way (see Hammer's comment)* did, in fact, unsubscribe him
(See: Matt Lake, "Opt-out attempts" CNet,
http://reviews.cnet.com/4520-3534_7-5020441-5.html?legacy=cnet&tag=st.mig.3227888-8-6602372-1.txt.3227888-8-6602372-5).

Similar opt-out experiment was conducted in this site, "Opt-out
'domain name' websites"
http://easyweb.easynet.co.uk/~gcaselton/spam/opt-out_domains.html -
please note, that one cannot know how many similar emails arrive from
seemingly different sources, and thus a "success" is declared although
none was really achieved. Also note, that on the looks of it, the
receiver did not do "Full Header" research, or a "Who is" research on
the spammer's details.

In July 2002, the Federal Trade Commission (FTC) announced that "In
April, the FTC warned 77 online marketers to discontinue their bogus
“unsubscribe” links or face possible legal action." (Source: FTC,
"Putting a Lid on Deceptive Spam"
http://www.ftc.gov/bcp/conline/features/spam.htm). In a research they
conducted in April 2002, they found that two-thirds of the "remove"
links or emails were invalid. However, of the remaining third, there
were surprisingly positive results in removing their address from
their list (Source: Joanna Glasner, "No Subscription for Spam Relief"
Wired News, http://www.wired.com/news/ebiz/0,1272,51517,00.html).
 
And what about those who do end up in real sites, with an "opt out"
possibility? This is what happened to Michael Rudas, who was directed
to a harvesting page (by mistake):
http://www.mdlug.org/archives/mdlug/msg16599.html a good point that is
mentioned in this thread, is that even if they are claiming that they
remove you from their list, it says nowhere that they oblige not to
give your name to another list.

To sum up, although the evidences are inconclusive, it seems that
usually you'll get a "dead" page of some sort, and that there is a
serious chance of getting more spam, or being harvested, if you
actually arrive to a valid page.

Spam House - Why you shouldn't click the "remove" link:
http://www.spamhaus.org/removelists.html

I hope this answers your question. I leave here my search strategy for
further research:
Spam "remove OR unsubscribe OR opt" live 
Spam "remove OR unsubscribe OR opt" alive 
"Opt out" spam "remove link" 
"Opt out" spam harvesting active
"Opt out" spam effective
"Opt out" spam
"Opt out" affectivity spam
"Opt out" affectivity 
"Unsubscribe requests" spam 
"Bogus remove" spam
"Bogus unsubscribe" spam
ftc spam valid "unsubscribe OR opt out OR remove" 
ftc spam "unsubscribe OR opt out OR remove


Read 2 Live comment is in "Since spam is an international
problem.............."
http://answers.google.com/answers/main?cmd=threadview&id=187342

If you need any further clarifications on this answer, please let me
know before you rate it.

Hi politicalguru, many thanks.  I think as much proof as I needed! 
Thanks also for the useful comments, Hammer and Pseud.  Much
appreciated.

I decided to test this theory about a year ago. I threw caution to the
winds and started religiously clicking every single opt-out link.

Here's what I discovered:
1. My spam load has shown a steady increase over the years regardless
of what I do, other than changes email addresses. I'm up to over 150
spam per day, every day.

2. At least 30% of the opt-out links were simply broken.

3. Of those not broken, around 50% led me through a maze of confusing
forms and ads trying to get to where I could actually opt out. In the
process, they set (or tried to set) cookies, and collected all sorts
of additional information. In many cases, at the end of the process,
the actual opt out submit button was ... BROKEN.

4. Some of the links appeared to opt me out. I'm not sure if they did,
because a lot of spam is templates that looks identical but always
comes from someone different. That particular spambot opted me out,
but passed me on to its five friends.

5. The reputable companies did actually seem to opt me out.
Unfortunately, their spam tended to be relatively inoffensive ads for
online stores that I shop at anyway.

Bottom line is that the opt out links appear to be useless at best
and, at worst, increase your spam.

- Hammer

I believe in the simple thumb rule -
If its a site that I had by mistake(or out of sheer stupidity) checked
the Subscribe option, then opt-out makes sense.
If its also a well known website (inclding the opt out address), then
this makes sense.
In all other cases, you are only confirming to a spammer, that this
email address is valid and inviting more spams.
However, this logic works only for those spam engines which use
automated tools to generate email ids, as in other cases they anyway
know its a genuine email id.

The question I have though with this theory is... "why?".  I'd
certainly agree with this if it cost money to send emails, as spammers
would want to minimize the cost and maximize effectiveness of their
techniques.  The reality is, though, that it costs spammers the same
amount whether to send 100 as it does to send a million emails and
they can often send up to 1 million emails per hour.

Why would they go through the time of developing the technology if
they can simply spam everyone?

My personal theory is that they include the "unsubscribe" links merely
to appear to be appear to be legitimate, to get advertising money with
pop-up/banner ads when you click on the link, and to possibly protect
themselves from any legal action (at least in their minds).

I think it's worth mentioning-- a lot of what you think might be spam
may not be. For example, most online stores have a checkbox when you
create your account to get on their mailing list. Then you start
getting info from them with sales, etc-- it LOOKS like spam but
technically speaking, it's a mailing list you signed yourself up for
and email you asked to receive. Just my 2c, as someone who sends out a
double-opt-in newsletter (i.e. you have to ask for my newsletter AND
then confirm that you asked in a 2nd step) and STILL gets flagged all
the time for (supposedly) sending spam! Ouch!