14.3 Using Other List Managers with Qmail

Although ezmlm is the list manager most often used with qmail, any list manager that's written to work with sendmail can easily be adapted to work with qmail. The most popular freeware packages are GNU Mailman, which has qmail config advice in README.QMAIL, and the Majordomo2 list manager, which has qmail support for lists in virtual domains built-in.^[5]

^[5] Majordomo1 is obsolete, and anyone thinking of using it should use majordomo2 instead. The commercial packages such as LISTSERV and Lyris include their own SMTP engine so they can run in parallel with qmail on a different virtual IP address, but they don't connect to qmail, or any other local MTA, directly.

14.3.1 Incoming Mail to List Managers

Mail sent to a list manager includes both the messages for the lists and the administrative mail to - -request addresses and the like. Systems with a small number of lists usually put sendmail alias entries for all of the entries into /etc/aliases. That also works with qmail, but can get unwieldy as the number of lists grows and if there are collisions between list names and usernames. Systems with lots of lists usually put the lists into virtual domains. Sendmail handles virtual domains differently from qmail, so the setup for qmail has to be a little different. List manager software is usually set-uid because it would difficult to control the UID for programs run from sendmail's /etc/aliases. With qmail, the virtual domain(s) for the list manager should belong to the list manager user, removing the need for set-uid except perhaps on CGI scripts for web interfaces. The individual list and administrative addresses can each be a .qmail file, or it might be easier to put them all in one file and use fastforward as described in Chapter 12.

14.3.2 Outgoing Mail from List Managers

List managers can hand mail to the MTA in two ways, by calling sendmail or SMTP. Using sendmail makes sense for administrative mail sent to a single recipient. It's a problem for list mail because the operating systems set a maximum total argument size in a call to sendmail or any other program, typically 64 K characters, which would limit lists to under 4,000 names. To get around this limit, the list manager can break the list up into sections and call sendmail multiple times or, more often, open an SMTP session to localhost, which permits an unlimited number of RCPT TO recipients. Either of these techniques works with qmail, although of course calling qmail-queue directly works better if a list manager has code to support it.

Some list managers can sort recipient addresses by domain and pass all the addresses in a domain together. This speeds up sendmail, which does domain or MX sorting internally, but doesn't help qmail. In fact, it can lead to somewhat unfortunate behavior; if qmail processes a message with a hundred recipients all in the same domain, it will open a large number of SMTP connections to that domain's mail server, which system managers misinterpret as an attempt to overload their system. If you can prevent your list manager from sorting its addresses by domain, do so.