Page 36 - Mercury Manual.book

31 Mailing lists
Mailing list settings and options

ommend that you consult your legal counsel and check what legal obligations you may have
regarding disclosure and record-keeping.

The Error Handling Page
If you've ever managed a large mailing list (one with 200 or more addresses) you'll know that
handling errors quickly becomes a significant problem: people change e-mail addresses with-
out unsubscribing from the list, domains change their names, temporary DNS problems result
in valid addresses bouncing for a day or two - all this and more results in tens or hundreds of
error notifications every time a message is sent to the list.

Unfortunately, the way the Internet's mail protocols work make it hard to come up with au-
tomatic ways of handling this kind of problem that aren't also very expensive in terms of the
bandwidth they use. In recognition of this, Mercury allows you to choose between three dif-
ferent ways of handling errors on your mailing lists.
1: Conventional error handling When this method is chosen, a single address is supplied as
the end point for errors in list mail. This address is placed in a special e-mail header called
the Return-Path, which all responsible mail programs should use when returning error noti-
fications. The result of this is that all "mail undeliverable" errors and other errors in sending
mail to the list will be redirected to this one address, the idea being that a single person will
be assigned the task of handling list errors manually. For smaller lists or lists where the per-
sonal touch is important, this approach usually works quite well, but it rapidly becomes un-
sustainable for larger lists.

2: VERP-based error handling VERP stands for Variable Envelope Return-path Process-
ing: when you use this method, every subscriber in the list gets a separate copy of every mes-
sage sent to the list, and in that copy of the message, a special version of the Return-path
field is created that allows Mercury to work out the individual list and subscriber from any
errors that get returned to it. Using this information, Mercury can automatically take certain
actions when errors occur, such as setting the subscriber's entry to "NOMAIL" or deleting the
subscription. Using VERP allows error handling to be almost entirely automated for a mail-
ing list, but it is very "expensive" in the sense that it generates an individual message for eve-
ry subscriber when a message is sent to the list. Even given the expense factor, however,
VERP is often the only manageable way of handling larger mailing lists. Note: when using Lists where VERP is ena-
VERP error handling, any value you enter in the Explode submissions into x jobs field of the bled always generate a
Distribution page of the Mailing List editor will be ignored - VERP-based mailing always separate message for
each subscriber.
generates a separate copy of every message for every subscriber on the list.

3: Hybrid error handling This approach combines both conventional error handling and
VERP-based error handling, and is a good compromise for medium-sized mailing lists. In hy-
brid mode, messages sent to the list are distributed normally and conventional error handling
(see above) is used to field errors arising from the distribution. Combined with this, however,
you can instruct Mercury that it should periodically send a specialized VERP mailing using
technique (2) above: this VERP mailing is called a probe, the idea being that the probe will
result in errors that will be handled automatically by Mercury. The advantage of Hybrid error
handling is that most of the mail sent to the list will go out normally, allowing the usual econ-
omies of scale associated with list mail, but the periodic VERP probe will automatically catch
and handle the majority of error conditions within a reasonable time frame. Mercury allows
you to create your own template file and use that to create the probe message. This means that
you can send out a monthly help guide to remind people how to manage their subscriptions
and so on, and have that guide double as your VERP probe.

Error handling scheme for this list's mail Choose between Conventional error handling,
VERP-based error handling or Hybrid error handling (see above for more details on the dif-