Entre le moment où j'écris cette phrase et le moment où elle sera publiée, le problème du spam sur Internet aura sûrement pris des proportions beaucoup plus importantes ou, en tout cas, on le ressentira comme tel. Il fut un temps, il n'y a pas si longtemps, où l'on pouvait créer une liste de diffusion sans avoir à prendre de mesures de protection contre le spam. De temps en temps, on pouvait recevoir un e-mail égaré, mais c'était suffisamment rare pour que cela reste peu gênant. Cette âge d'or est révolu. De nos jours, une liste de diffusion qui ne se prémunie pas du spam sera rapidement noyée sous les e-mails indésirables, au point qu'elle en devienne inutilisable. Les protections contre le spam sont indispensables.

On peut séparer les protections contre le spam en deux catégories : celles qui empêchent les courriers indésirables d'apparaître sur la liste de diffusion et celles qui protègent les listes de diffusions contre les collecteurs d'adresses des spammeurs. La première étant la plus importante, c'est celle que nous allons détailler en premier.

List subscribers often want to put mails from the list into a project-specific folder, separate from their other mail. Their mail reading software can do this automatically by examining the mail's headers. The headers are the fields at the top of the mail that indicate the sender, recipient, subject, date, and various other things about the message. Certain headers are well known and effectively mandatory:

From: ...
To: ...
Subject: ...
Date: ...

Others are optional, though still quite standard. For example, emails are not strictly required to have the

Reply-to: sender@email.address.here

header, but most do, because it gives recipients a foolproof way to reach the author (it is especially useful when the author had to send from an address other than the one to which replies should be directed).

Some mail reading software offers an easy-to-use interface for filing mails based on patterns in the Subject header. This leads people to request that the mailing list add an automatic prefix to all Subjects, so they can set their readers to look for that prefix and automatically file the mails in the right folder. The idea is that the original author would write:

Subject: Making the 2.5 release.

but the mail would show up on the list looking like this:

Subject: [discuss@lists.example.org] Making the 2.5 release.

Although most list management software offers the option to do this, I strongly recommend against turning the option on. The problem it solves can easily be solved in much less obtrusive ways, and the cost of eating space in the Subject field is far too high. Experienced mailing list users typically scan the Subjects of the day's incoming list mail to decide what to read and/or respond to. Prepending the list's name to the Subject can push the right side of the Subject off the screen, rendering it invisible. This obscures information that people depend on to decide what mails to open, thus reducing the overall functionality of the mailing list for everyone.

Instead of munging the Subject header, teach your users to take advantage of the other standard headers, starting with the To header, which should say the mailing list's name:

To: <discuss@lists.example.org>

Any mail reader that can filter on Subject should be able to filter on To just as easily.

There are a few other optional-but-standard headers expected for mailing lists. Filtering on these is even more reliable than using the "To" or "Cc" headers; since these headers are added to each post by the mailing list management software itself, some users may be counting on their presence:

list-help: <mailto:discuss-help@lists.example.org>
list-unsubscribe: <mailto:discuss-unsubscribe@lists.example.org>
list-post: <mailto:discuss@lists.example.org>
Delivered-To: mailing list discuss@lists.example.org
Mailing-List: contact discuss-help@lists.example.org; run by ezmlm

For the most part, they are self-explanatory. See http://www.nisto.com/listspec/list-manager-intro.html for more explanation, or if you need the really detailed, formal specification, see http://www.faqs.org/rfcs/rfc2369.html.

Notice how these headers imply that if you have a mailing list named "list", then you also have administrative addresses "list-help" and "list-unsubscribe" available. In addition to these, it is normal to have "list-subscribe", for joining, and "list-owner", for reaching the list administrators. Depending on the list management software you use, these and/or various other administrative addresses may be set up; the documentation will have details. Usually a complete explanation of all these special addresses is mailed to each new user as part of an automated "welcome mail" on subscribing. You yourself will probably get a copy of this welcome mail. If you don't, then ask someone else for a copy, so you know what your users are seeing when they join the list. Keep the copy handy so you can answer questions about the mailing list functions, or better yet, put it on a web page somewhere. That way when people lose their own copy of the instructions and post to ask "How do I unsubscribe from this list?", you can just hand them the URL.

Some mailing list software offers an option to append unsubscription instructions to the bottom of every post. If that option is available, turn it on. It causes only a couple of extra lines per message, in a harmless location, and it can save you a lot of time, by cutting down on the number of people who mail you—or worse, mail the list!—asking how to unsubscribe.

Earlier, in la section intitulée « Évitez les discussions privées », I stressed the importance of making sure discussions stay in public forums, and talked about how active measures are sometimes needed to prevent conversations from trailing off into private email threads; furthermore, this chapter is all about setting up project communications software to do as much of the work for you as possible. Therefore, if the mailing list management software offers a way to automatically cause discussions to stay on the list, you would think turning that feature on would be the obvious choice.

Well, not quite. There is such a feature, but it has some pretty severe disadvantages. The question of whether or not to use it is one of the hottest debates in mailing list management—admittedly, not a controversy that's likely to make the evening news in your city, but it can flare up from time to time in free software projects. Below, I will describe the feature, give the major arguments on both sides, and make the best recommendation I can.

The feature itself is very simple: the mailing list software can, if you wish, automatically set the Reply-to header on every post to redirect replies to the mailing list. That is, no matter what the original sender puts in the Reply-to header (or even if they don't include one at all), by the time the list subscribers see the post, the header will contain the list address:

Reply-to: discuss@lists.example.org

On its face, this seems like a good thing. Because virtually all mail reading software pays attention to the Reply-to header, now when anyone responds to a post, their response will be automatically addressed to the entire list, not just to the sender of the message being responded to. Of course, the responder can still manually change where the message goes, but the important thing is that by default replies are directed to the list. It's a perfect example of using technology to encourage collaboration.

Unfortunately, there are some disadvantages. The first is known as the Can't Find My Way Back Home problem: sometimes the original sender will put their "real" email address in the Reply-to field, because for one reason or another they send email from a different address than where they receive it. People who always read and send from the same location don't have this problem, and may be surprised that it even exists. But for those who have unusual email configurations, or who cannot control how the From address on their mails looks (perhaps because they send from work and do not have any influence over the IT department), using Reply-to may be the only way they have to ensure that responses reach them. When such a person posts to a mailing list that he's not subscribed to, his setting of Reply-to becomes essential information. If the list software overwrites it, he may never see the responses to his post.

The second disadvantage has to do with expectations, and in my opinion is the most powerful argument against Reply-to munging. Most experienced mail users are accustomed to two basic methods of replying: reply-to-all and reply-to-author. All modern mail reading software has separate keys for these two actions. Users know that to reply to everyone (that is, including the list), they should choose reply-to-all, and to reply privately to the author, they should choose reply-to-author. Although you want to encourage people to reply to the list whenever possible, there are certainly circumstances where a private reply is the responder's prerogative—for example, they may want to say something confidential to the author of the original message, something that would be inappropriate on the public list.

Now consider what happens when the list has overridden the original sender's Reply-to. The responder hits the reply-to-author key, expecting to send a private message back to the original author. Because that's the expected behavior, he may not bother to look carefully at the recipient address in the new message. He composes his private, confidential message, one which perhaps says embarrassing things about someone on the list, and hits the send key. Unexpectedly, a few minutes later his message appears on the mailing list! True, in theory he should have looked carefully at the recipient field, and should not have assumed anything about the Reply-to header. But authors almost always set Reply-to to their own personal address (or rather, their mail software sets it for them), and many longtime email users have come to expect that. In fact, when a person deliberately sets Reply-to to some other address, such as the list, he usually makes a point of mentioning this in the body of the message, so people won't be surprised at what happens when they reply.

Because of the possibly severe consequences of this unexpected behavior, my own preference is to configure list management software to never touch the Reply-to header. This is one instance where using technology to encourage collaboration has, it seems to me, potentially dangerous side-effects. However, there are also some powerful arguments on the other side of this debate. Whichever way you choose, you will occasionally get people posting to your list asking why you didn't choose the other way. Since this is not something you ever want as the main topic of discussion on your list, it might be good to have a canned response ready, of the sort that's more likely to stop discussion than encourage it. Make sure you do not insist that your decision, whichever it is, is obviously the only right and sensible one (even if you think that's the case). Instead, point out that this is a very old debate, there are good arguments on both sides, no choice is going to satisfy all users, and therefore you just made the best decision you could. Politely ask that the subject not be revisited unless someone has something genuinely new to say, then stay out of the thread and hope it dies a natural death.

Someone may suggest a vote to choose one way or the other. You can do that if you want, but I personally do not feel that counting heads is a satisfactory solution in this case. The penalty for someone who is surprised by the behavior is so huge (accidentally sending a private mail to a public list), and the inconvenience for everyone else is fairly slight (occasionally having to remind someone to respond to the whole list instead of just to you), that it's not clear that the majority, even though they are the majority, should be able to put the minority at such risk.

I have not addressed all aspects of this issue here, just the ones that seemed of overriding importance. For a full discussion, see these two canonical documents, which are the ones people always cite when they're having this debate:

Despite the mild preference indicated above, I do not feel there is a "right" answer to this question, and happily participate in many lists that do set Reply-to. The most important thing you can do is settle on one way or the other early, and try not to get entangled in debates about it after that.

The technical details of setting up mailing list archiving are specific to the software that's running the list, and are beyond the scope of this book. When choosing or configuring an archiver, consider these qualities:

The above is just a technical checklist to help you evaluate and set up an archiver. Getting people to actually use the archiver to the project's advantage is discussed in later chapters, in particular la section intitulée « Conspicuous Use of Archives ».

Here are some open source tools for doing list management and archiving. If the site where you're hosting your project already has a default setup, then you may not ever have to decide on a tool at all. But if you must install one yourself, these are some possibilities. The ones I have actually used are Mailman, Ezmlm, MHonArc, and Hypermail, but that doesn't mean the others aren't good too (and of course, there are probably other tools out there that I just didn't happen to find, so don't take this as a complete list).

Mailing list management software:

Mailing list archiving software: