Reply-to-List, or Reply-to-All?

There is an open question about the best "netiquette" to use when replying to mailing list messages — should you use "Reply to All" and include the original sender of the message and all other recipients well as the list, or should you use "Reply to List" and send your message only to the list?

Note that this is not the same topic as discussed in Chip Rosenthal's "Reply-To" Munging Considerered Harmful" essay. That essay is about what the list should do, while this page talks about your choices as the user who is replying to the mail.

Background

Different people have different preferences, use different software, and have different ways of processing their incoming mail. For example:

Fred filters all incoming messages into separate folders according to the list it comes from. If you send a message which is cross-posted to two lists that he's subscribed to, and Cc him directly because you know he has a personal interest and you don't know that he's subscribed (or suspect he might not be looking in those folders very often), then he will have separate copies in each list folder, in addition to the copy in his INBOX.
John doesn't do any filtering — he isn't subscribed to many mailing lists, so hasn't bothered to work out how to do it. If you Cc him on a message which is also sent to a list he's on, then he'll see two copies of that message in his INBOX.
Mary has configured her mail software so that it automatically filters out "duplicates", depending on a Message-Id: header which is supposed to be unique in all email messages. So she'll only ever see one copy of the message, usually the one which arrives first.
(If she's included directly in Cc then the direct copy is fairly sure to be the first to arrive, so she'll only get the copy in her INBOX. If she's not in Cc and the message is sent to more than one mailing list that she's on, then she'll only see the copy which arrives from whichever mailing list is fastest. If she filters list mail into folders, it's basically random which list folder it goes into.)
Claire is not subscribed to the list at all. She's been added to Cc because she has an interest in this particular discussion, and can offer expert advice even though she's not usually involved with this project at all.
Karl is not subscribed to the same list as you; he's subscribed to a different mailing list. If you are participating in a discussion which crosses project boundaries and is cross-posted to more than one list, he will only see messages which are posted to the list he's subscribed to.

Each of these people may have different preferences — it's hard to know what to do for the best, and whether to include them in Cc or not when you reply to their messages.

Obviously if they have told you their preference, then that's not so hard — just do as they ask. But most of the time you don't know; you have to guess. And when we're working on mail software, we have to set the default behaviour for a non-private reply. That's what prompted me to write this page.

Pros and Cons

Let's look at what goes wrong if you make the wrong choices... If you choose 'Reply to All', then everybody will get a copy. That may annoy John and Mary a little bit, because...

John will receive two copies of the mail in his INBOX.
Mary will receive the mail in her INBOX and not in the list folder.

If you choose 'Reply to List', then your reply will go just to one address; a mailing list address. In the case of cross-posted messages, which list that is will depend on which copy of the message you reply to. If you're like Mary and you filter "duplicates", that basically means that you'll continue the discussion on whatever list has the fastest mailing list software. So what happens is...

Claire is dropped from the discussion completely, because you dropped her from Cc.
Karl is dropped from the discussion completely, along with everyone else on that mailing list.
John and Mary are happy.
Fred may or may not see the discussion; depending on how often he looks into the folder for the list you happened to reply to.
Because list software can often be slow, the active participants may experience a long delay before seeing your response — so by the time they have the chance to reply, the discussion may have moved on and they may have missed their chance.

Your decision

You may not have spent too much time thinking about the different ways that people handle email; hopefully the above has given you some pointers.

Now it's time for you to make your own decision — if you don't know what the sender prefers, which one do you guess?

The corollary to the same question is: If you're working on a mail program, what should you make the default behaviour, if the user doesn't express a preference?

I've tried to stick to the facts so far and not offer my opinion. If you don't want to know what I think, you can look away now...

To me, the answer seems obvious when you look at the failure modes:

If you "Reply to All" then some people may get a second copy of the message... not really the end of the world.
If you "Reply to List" then some people could be cut out of the discussion completely, and for a cross-posted discussion you risk splitting the thread into separate discussions on different lists.

Yes, it's true that in Mary's case if you "Reply to All" then she might miss the copy of the mail in her list folder, as it'll arrive in her INBOX instead. But it's a fairly safe bet that she'll see it there anyway, and she can always move it to the list folder if she wants to. It's still not much of an issue; at least she has it.

Besides, Mary ought to be used to messages not being in the right list folder anyway. As described above, her setup means that if a message is sent to more than one mailing list that she's subscribed to, she'll get only one copy of that message — in an essentially random choice of list folders depending on which list is faster. That was her choice.

(There's a strong argument that Mary's mail setup is broken, because you can't really depend on the Message-Id: header being unique. For fun, try sending messages to various people "including" Mary, but make the Message-Id: the same on all of your messages. Mary will only see the first, and you can say what you like about her after that, while other people think she's in Cc. You can also prevent her from receiving list messages you don't want her to see, if you were included directly in Cc so you get them before she does. You just need to quickly send her a different message with the same Message-Id: as the message you want her to miss — as long as yours gets there first, her mail software will helpfully delete the message you didn't want her to see.)

So really, the decision is a no-brainer. Unless you know that the other people involved in the discussion are like Mary or John, then you should always play it safe and use "Reply to All".

Deliberately replying only to the list and cutting others out of the discussion is considered to be extremely rude by some people.

Public vs. Private replies

So far, I've only spoken about the case where you know you want to reply in public. When we're thinking about what mail software should do, and what the default behaviour should be, we also have to consider the question of "public or private?". This one takes even less thought, and again the decision can be based entirely on the failure modes:

If you send a private reply when the user expected it to be public, that is easy to fix — just forward or resend the message to the correct place.
If you send a public reply when the user expected it to be private, the effects of that can be catastrophic — the public message can never be retracted, and could be extremely damaging.

So although people have occasionally asked for the default 'Reply' button and the associated 'Reply to Sender' menu option to actually reply to the list for list messages, that seems like a really bad idea — and most of the time they realise this when it's pointed out to them.

Any decent mail program will have separate options for a private reply, vs. a more public reply — and the private reply option should never trick you into replying back to the list.

Reply-To: list

For mailing list administrators, this is probably a reasonable time to refer back to the Reply-To-Harmful essay that I mentioned in the second paragraph. Setting a Reply-To: address to point back to the list is doing the wrong thing in both ways. It's hijacking my private "Reply" button and making it give a public reply, when I already had a button that I could use if I wanted to make a public reply. And it's even giving the wrong type of public reply — it's replying only to the list, instead of to all the correspondents.

Please, never set a mailing list to have a Reply-To: header point back to the list. That's like sending me a virus which infects my mail program and hacks it so that it replies in public when I specifically pressed the button which should give me a private reply. If I wanted to send a public reply, the button for that is right next to the one I pressed! If I'd wanted that, I would have pressed it. Thankfully, I now have this to save me:

Evolution

This is what we currently have in Evolution: a private Reply button, and a 'Group Reply' button which gives you a dropdown choice of Reply-to-All vs. Reply-to-List.

You don't have to use the drop-down menu, of course — if you just click 'Group Reply', it'll do the sane default which is Reply-to-All. You can go into the preferences and change the default to be Reply-to-List. Please don't, though.