2.6 The Digest Options Category

Digest delivery is a way to bundle many articles together into one package, which can be delivered once per day (if there were any posted articles), or whenever the package is bigger than a specified limit. Some users may prefer this style of delivery for higher traffic lists since they will receive fewer messages.

Mailman supports two standard digest formats, and if digests are enabled, users can select which of the two formats they receive. One is MIME digests, where each message is an attachment inside a multipart/digest. This format also contains a summary table of contents, and of course the an optional header and footer, and it retains most of the headers of the original messages.

The second type is called ``plaintext'' digests because they are readable in mail readers that don't support MIME. Actually, they adhere to the RFC 1153 digest standard. The retain some, but not all of the original messages, but can also include a summary and headers and footers.

Like non-digest delivery, you can enable or disable digest delivery, but you cannot disable both types of delivery. You can specify different headers and footers for digest and non-digest deliveries. You cannot personalize digest deliveries.

As list administrator, you may want to send an urgent message to all list members, bypassing the normal digest bundling. To do this, send the message with a Urgent: header, where the value of the header is the list administrator's password. Non-digest members will receive the message like normal, but digest members will receive the message immediately⁵.

Here are the variables which control digest delivery:

digestable: The option controls whether members can receive digest deliveries or not. If not, they will be forced to receive immediate deliveries. You can't disable digests if non-digests are already disabled.
digest_is_default: Controls which style of delivery is the default for new members. You can choose Regular (non-digest) or Digest delivery.
mime_is_default_digest: If a member is allowed to choose digests, this variable controls which is the default digest style they will receive. Plain digests are RFC 1153 format as described above.
digest_size_threshold: Normally, digest members get at least one message per day, if there have been any messages posted to the list. However, for high volume lists, you may want to send out digests when the size has reached a certain threshold, otherwise, the one digest they receive could be huge. This variable controls the size threshold by specifying the maximum digest size in kilobytes. Note that this threshold isn't exact. Set this variable to zero to specify that there is no size threshold, in which case no more than one digest will be sent out per day.
digest_send_periodic: This variable actually controls whether or not a digest is sent daily when the size threshold has not yet been met. If set to No, then digests will only be sent when they are bigger than digest_size_threshold.
digest_header: This text box lets you enter information that will be included in the header of every digest message sent through the list. The same information can go in this header as can go in the msg_header, except for the personalization variables.
digest_footer: Just like with the header, you can add a footer to every message. The same rules apply to digest footers as apply to digest headers.
digest_volume_frequency: Each digest is numbered with a volume and an issue. This variable controls how often a new digest volume is sent. When the digest volume number is incremented, the issue number is reset to 1.
_new_volume: This is an action variable, which forces an increment of the volume number as soon as you submit the form.
_send_digest_now: This is another action variable. Select Yes, submit the form, and the current digest is packaged up and sent to digest members, regardless of size (well, there has to be at least one message in the digest).

Footnotes

... immediately ⁵: They'll also receive the message in the digest.