PEAK Internet Mail Lists

Anatomy of a Disaster

Soooo, you want a mail list? They are very useful, and pretty much required if you regularly
send mail out to a large number of people (more than a couple dozen). They can also bite you
big time if you’re not careful. A scenario we’ve had happen a number of times plays out like
this: someone creates a new list, immediately adds 10,000 addresses to the list and sends out
mail that basically says “we think you’ll love this great new list, but if not just unsubscribe”.
Most of the recipients have no experience with mail lists and reply to the list “get me off this
list!” which triggers a cascading flurry of similar replies, all to the list and everyone ignoring
the footers which tell them how they can unsubscribe without bothering everyone else. Within a
day, we’ve had to shut off the list and everyone retreats to their corner shaking from the

Fortunately, it’s fairly easy to avoid that worst-case scenario:

Recipe for Success

The list software we use is called Mailman. It’s very¬†powerful, yet still pretty easy to use. Because it’s powerful, the number of configuration
options is rather overwhelming. Fortunately, only a few are significant for most users:

Reply to sender– Mail lists are configured in one of two ways:
  1. Reply to list – The from address is the address of the list. This allows
    people to simply hit “Reply” and participate in the list discussion.There is also a particular disadvantage to this however: people have a habit of hitting
    reply and dashing off something quick without a lot of thought, and all too often it may be
    personal and/or embarrassing, particularly when sent to a large group of people. Careers
    and relationships have been ruined by sending something to a list accidentally when they
    meant a private reply. This is also what sets off the cascading failure in the introductory
  2. Reply to sender – As a result, the recommended setting for lists is that a
    default reply goes back to only the sender of the original message. Replies can still be
    sent to the list by using the Group Reply command that virtually all mail clients have, but
    that shouldn’t be the default, so accidental replies are “fail safe”, in that they minimize
    the damage. In particular, this avoids the scenario above of cascading list traffic
    (though the list owner will still probably get flooded with unsubscribe requests, at
    least there won’t be collateral damage to everyone on the list).The main disadvantage
    of this has to do with a recent anti-spam feature called “SPF” (Sender Permitted From).
    Domains that have this feature enabled list the mail servers that are allowed to send mail
    from them, and random list servers aren’t generally in the list. As a result, recipient
    mail servers that check SPF data will flag or reject mail list mail sent by users of those
    domains. There is a simple solution however: list recipients on such servers just need to
    whitelist the mail list servers they subscribe to.

    Another minor disadvantage to this setting is that users have a habit of not weeding out
    duplicate addresses: discussion participants will frequently get two copies of replies:
    one to them directly, and another when the copy to the list gets sent out. This is,
    however, much smaller “collateral damage” than occurs from a cascading list failure.

    Once a list is established, it may be desirable to switch the list back to “reply to list”
    to avoid these disadvantages, but careful consideration should be done before doing so.

Moderated list
By default, all new lists are setup to be “moderated”. This
means that whenever a list member posts to the list, the message is held for review and
the list administrator must approve it before it goes out. If the list is being setup for
one or a few people to send announcements, you’ll want to leave the list setup this way.
If the list is intended for discussion, then you may want to turn off moderation, though it
is highly recommended that if you’re populating with a lot of addresses of people
not expecting it, you should leave the list moderated for a few posting cycles to make sure
you don’t have a cascading failure. The setting for this is a little ambiguous: in the
mailman menus, go to =Privacy options=, then =Sender filters=. The first option, =By
default, should new list member postings be moderated?= is the setting you want. To require
postings to be reviewed, select =Yes=, for free flow discussion, select =No=. You can also
require postings from questionable list members individually by checking the “mod” box in
the =Membership Management/Membership List= menu.
Start Small
While this isn’t really a “configuration” setting, if you’re planning
on prepopulating the list with a large number of addresses, start with a couple dozen,
particularly if they’re not expecting to be subscribed. Ramp up carefully as you get a feel
for running a list. This will avoid having a small problem turn into a nightmare… 

Review your settings after a while
Finally, once the list has been going a bit, go back through the setting options again.
Many will probably make more sense. There is also a
List Administration
that will give you an overview of what the settings actually mean, which should
help.If you have any questions, email and we’ll be glad to help you out.