CC considered harmful (was Re: [linux-elitists] [RANT] Debian the Elitist Distribution?)

Aaron Sherman
Mon Feb 23 09:02:47 PST 2004

On Mon, 2004-02-23 at 09:04, Andrew wrote:
> > Tell that to people who are on list digests, or tired or waiting for slow
> > list servers.
> That's their own problem.  They can also include a signature line that says 
> "I'm a dumbass on a digest list/slow list server, please CC me directly."  
> In my own skewed perception of reality I conclude that people who are 
> communicating via mailing lists prefer to have the communication stay on 
> the list.

Well, since it's been brought up, and the usual round of "but I want my
mailbox to be the way I want it" responses are all in place, let me
analyze this from a technical standpoint:

To start at the high level, the CC/TO distinction is semantic. There is
no difference in the way the mailer will handle these messages (and the
SMTP envelope will be the same when it reaches your mailbox regardless
of which header slot you were in).

Given that, we should treat these as semantic tags that we add for
reasons that we agree are meaningful.

One piece of signal-rich information that I think we can all agree is
conveyed by the TO vs. the CC header is WHO I am speaking to, vs. who I
am including in "earshot" of that conversation.

When responding to a message, it's easy to decide who the recipient is
by imaginging that you start off the message with "dear X,". Whoever X
is, that's your TO line. If that is a mailing list (as with this
message), then that's who you should address, and there is no need to CC
anyone else (unless you know them to be off-list, and are including them
for some other reason) -- so in that respect, no, you should not CC
people who are on the list, as that's semantically null or at least very
light on meaning.

If you are addressing a single person, but wish the thread of
conversation to stay on the list, then it seems to me that the correct
way to imply that is to send TO that person and to CC the list. You
might do this, for example, if you are specifically asking that person
for a response (e.g. "why did you think X, isn't that refuted in Y?")

This allows mail filters, digests, and many other sorts of "mail magic"
to behave correctly. I for example, will often reply faster to a
question posed to me if it is sent TO me and CC perl5-porters, even
though I'm on that list. In fact, I might never notice the message on
p5p even in a thread I participated in, because I'm simply not paying
THAT close attention.

I hope this information is helpful in making rational choices.

However, I would still prefer that anyone who feels so strongly about
CCing as to regularly threaten a mailing list with blocking individual
people's mail... simply do so and get past it. In fact, while you're at
it clap your hands over your ears and yell, "neener neener!" ;-)

Aaron Sherman <>
Senior Systems Engineer and Toolsmith
"It's the sound of a satellite saying, 'get me down!'" -Shriekback

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