From b5896ba9f6047e7031e2bdee0622d543e11a6734 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 6 May 2024 03:46:30 +0200 Subject: Adding upstream version 3.4.23. Signed-off-by: Daniel Baumann --- src/local/Musings | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) create mode 100644 src/local/Musings (limited to 'src/local/Musings') diff --git a/src/local/Musings b/src/local/Musings new file mode 100644 index 0000000..6149a2e --- /dev/null +++ b/src/local/Musings @@ -0,0 +1,39 @@ +Local delivery models + +The "monolithic" model: recursively expand the complete initial +recipient list (via aliases, mailing lists, .forward files) to one +expanded recipient list (mail addresses, shell commands, files, +mailboxes). Sort/uniq the expanded recipient list, and deliver. + +The "forward as if sent by recipient" model: each level of recursion +(aliases, mailing lists, forward files) takes one entire iteration +through the mail system. Non-recursively expand one local recipient +(via alias, mailing list, the recipient's .forward file) to a list +of expanded recipients. Sort/uniq the list and deliver by re-injecting +messages into the mail system. Since recipient expansion uses a +non-recursive algorithm, the mailer might loop indefinitely, +re-injecting messages into itself. These local forwarding loops +must be broken by stamping a message when it reaches the local +delivery stage (e.g., by adding a Delivered-To: message header). + +The Postfix system uses a hybrid approach. It does recursive alias +expansion, but only one initial recipient at a time. It delivers +to expanded recipients by re-submitting the message into the mail +system, so it can keep track of the delivery status for each expanded +recipient. Because alias expansion does not look in .forward files, +it cannot prevent local forwarding loops. The Postfix system adds +Delivered: message headers to break local and external forwarding +loops. + +Delivery status management + +The "exact" model: maintain on file the delivery status of each +expanded recipient: remote recipients, shell commands and files, +including the privileges for delivery to shell commands and files. + +The "safe" model: maintain on file only the delivery status of +non-sensitive destinations (local or remote addresses). Deliver to +sensitive destinations first (commands, files), but do not keep a +record of their status on file (including privileges). This means +that the mail system will occasionally deliver the same message +more than once to a file or command. -- cgit v1.2.3