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OpenBSD Mailing List Server
Introduction to List Moderation When people say "a mailing list is moderated," they usually mean that every message that someone posts to the list is examined by someone else before it is allowed to be delivered. In Majordomo, moderation can also apply to subscription or unsubscription, access to the list archives, and many of Majordomo's other features. The word "request" is used to refer to anything that requires approval, including posted messages. When a request is moderated, Majordomo mails a message to the moderators with the word "CONSULT" in the subject line. Basically, to approve or discard a request, you only need to reply to that message and type one of these two commands into the body of the reply: accept reject The rest of this document focuses on the details of moderation: * Who are the moderators? * How does Majordomo keep track of the moderated requests? * Why does a request become moderated? * Is the person who made the request notified of what happens? * How can you decide what requests are and are not moderated? * How can messages be discarded automatically instead of moderated? The last section of this document presents solutions for common moderation problems. The examples in this document assume that you know how to use your list's administrative password. Please review "help admin_passwords", if you have not already done so. In each example, replace LISTNAME with the name of your mailing list. Replace ADDRESS with a valid e-mail address. What's the difference between an owner and a moderator? ------------------------------------------------------- The short answer is that the owner has all of the authority, and the moderator has all of the responsibility. Only kidding. When a request is moderated, a message with CONSULT in the Subject header will be sent to the moderators. Basically, all the moderators have to do is reply with the accept command to approve a request, or the reject command to disallow it. Neither of these commands requires a password, so in principle the moderators might not have permission to perform other administrative tasks, such as unsubscribing people from the mailing list. The list owners are the people whose e-mail addresses appear in the "owners" configuration setting. The list owners usually know the list's master password, and can issue any administrative command. Majordomo uses the following steps to determine who the moderators are, stopping when it finds a valid address: 1. It looks in the LISTNAME:moderators auxiliary list, for addresses that do not have the "nomail" flag set (see "help auxiliary_list" for more details). 2. It looks in the "moderators" configuration setting for the list. 3. It looks in the "owners" configuration setting. 4. It looks in the "whoami_owner" configuration setting. If the moderators and the owners are different people, and the owners want the moderators to be able to perform other duties, such as subscribing and unsubscribing people, passwords with restricted privileges can be defined for the moderators using the "passwords" configuration setting (See "help configset_passwords" for more details). Token identifiers ----------------- When a request requires someone's approval, Majordomo creates a random number, called a "token identifier" or "token," to keep track of the request. Every token looks something like this: 98FE-03BB-A743 To approve or disallow a token, the accept or reject command is used, for example: accept B139-DE29-A649 reject 98FE-03BB-A743 If a request is not accepted or rejected, after a few days the moderators will receive a reminder that the request has not been completed. A few days later, the token will expire, and the request will never be completed. The reminder notice gives a brief summary of the request. If a moderator has forgotten the details of the request, the tokeninfo command can be used to obtain more information, for example: tokeninfo 9F34-77DA-B021 The accept, reject, and tokeninfo commands never require a password. Administrators who do know a list's administrative password can see a summary of outstanding tokens for a mailing list with the showtokens command: showtokens LISTNAME See "help accept", "help reject", "help showtokens", and "help tokeninfo" for more details. Notifications ------------- When a moderator accepts or rejects a request, Majordomo may or may not send a notice to the person affected by the request (the "victim"). The decision to send a notice is based upon the victim's personal settings. * For accepted requests other than posted messages, a notice is always sent. * When posted messages are accepted, a notice is sent if the "ackpost" setting is turned on. * When any request is rejected, a notice is sent if the "ackreject" setting is turned on. If the victim is a subscriber to the mailing list, the settings are determined by the victim's settings. Otherwise, the settings are determined by the list's nonmember_flags configuration setting. See "help set" and "help configset_nonmember_flags" for details on changing those settings. Causes of moderation -------------------- There are many ways in which the rules in the access_rules configuration setting can cause moderation. These causes will usually be clear to the person writing the rules. However, there are some less-than-obvious ways in which the default access settings can cause a request to be moderated. For requests other than posted messages, the default settings are usually determined by a "policy" or "access" configuration setting. For example, access to the subscribe command is controlled by the subscribe_policy configuration setting, and access to the who command is controlled by the who_access configuration setting. All of the policy and access settings are part of the ACCESS category. To see their values, use this command: configshow LISTNAME ACCESS (Substitute the name of your mailing list for LISTNAME, but type the word ACCESS as shown, in capital letters.) If a policy setting is "open" or "open+confirm," the moderators' approval will be needed if there is an address mismatch or posing. A mismatch occurs when someone issues a command for another address. For example, if firstname.lastname@example.org uses this command: subscribe LISTNAME email@example.com the two addresses, firstname.lastname@example.org and email@example.com, do not match. Posing occurs when someone uses the "default user" command. For example, if firstname.lastname@example.org uses these commands: default user email@example.com subscribe LISTNAME firstname.lastname@example.org is posing as email@example.com. Mismatch and posing also will cause messages posted with the post command (see "help post" for more details) to be moderated. Aside from mismatch and posing, there are many reasons a posted message might be moderated: * The moderate configuration setting is turned on. * The author of the message is not a member of the groups in the restrict_post configuration setting. * The administrivia configuration setting is turned on, and the message matches one or more of the patterns in the admin_body and admin_headers configuration settings. * The message contains an Approved: header with an invalid password. * The message exceeds one of the size limits in the max_total_header_length, maxlength, max_header_line_length, and max_mime_header_length configuration settings. * The message has a body part whose type is marked for moderation by the attachment_rules setting. * The message has a duplicate Message-ID header, or duplicate body, of another message that has been posted to the same mailing list. * The message matches one or more of the patterns in the taboo_body and taboo_headers configuration settings. * The author exceeded the "soft limit" quota in the post_limits configuration setting. * The "postblock" personal setting for the author is turned on. (See "help set" for details on personal settings.) * The e-mail address in the "From" header of the message is invalid. The rest of this document discusses how these settings can be tuned for effective moderation of posted messages. Using the access_rules setting, any or all of the moderation checks can be turned off. Likewise, any of the moderation checks can cause a message to be discarded instead of moderated. See "help configset_access_rules" for more details. Full moderation --------------- The simplest way to moderate every message posted to a mailing list is to turn on the moderate configuration setting: configset LISTNAME moderate = 1 See "help configset_moderate" for more details. The simplest way to moderate every message posted by one subscriber is to turn on the "postblock" setting for that subscriber: set LISTNAME postblock firstname.lastname@example.org See "help set" for more details about personal settings. Content filtering ----------------- There are six configurations settings that support moderation based upon the contents of the message. For more information, see the following documents: help configset_admin_body help configset_admin_headers help configset_administrivia help configset_attachment_rules help configset_taboo_body help configset_taboo_headers Size limits ----------- There are four configuration settings that support moderation based upon the size of the message body or the message headers. For more information, see the following documents: help configset_max_header_line_length help configset_max_mime_header_length help configset_max_total_header_length help configset_maxlength Personal limits --------------- There are two moderation checks that depend upon the address of the author of a posted message. A message will be moderated if the author's "postblock" personal setting is turned on. Only subscribers have personal settings, so if a non-subscriber posts a message, it will be moderated if the "postblock" flag is included in the nonmember_flags configuration setting. Unless the postblock setting is listed in the default_flags configuration setting, a subscriber can unsubscribe, then subscribe again to turn the setting off. For more information on the postblock setting, see "help set". The post_limits configuration setting is used to moderate or deny messages from people who post too often. The limits can vary from person to person or domain to domain. For example, consider the following command: configset LISTNAME post_limits <<BLD /example.edu/ | 10/100 | 4/d /./ | 15/100 | 7/d BLD These settings establish the following limits: * For addresses in the example.edu domain, any person who has posted more than 10 messages out of the last 100 will exceed the "soft limit." Any person who has posted more than 4 messages in the last day will exceed the "hard limit." * For all other addresses, the soft limit is 15 messages out of the last 100, and the hard limit is 7 messages in the last day. Exceeding a soft limit will cause a message to be moderated. Exceeding a hard limit will cause a message to be denied and discarded. For more information, see "help configset_post_limits". Duplicates ---------- Two posted messages are considered duplicates if at least one of the following three criteria is true: * The messages have duplicate Message-ID headers. * The first body parts of the messages are identical. * The first 10 lines of each message's body are identical. By default, any message that duplicates a previously posted message will be moderated. Although these checks are useful for preventing mail loops, they can also unnecessarily moderate messages that have a first body part that is empty. To turn off the body checks, use the following rule in the access_rules setting: post unset=dup_checksum, unset=dup_partial_checksum ALL "Approved" messages ------------------- Anyone who knows a list's master password can use the password to skip all of the access checks. To do this, it is necessary to add an "Approved" line in the headers or body of the message. For example, if the list's master password is 4a5p6h7o, the line would look like this: Approved: 4a5p6h7o This line can appear in the message headers, or as the first non-blank line in the body of the message. Majordomo will automatically remove the Approved line when the message is delivered. For compatibility with Majordomo version 1, if an "Approved" line in the body is followed by a non-blank line, it and all succeeding non-blank lines, up to the first blank line, will become the headers of the message when it is posted. Sometimes, a moderator may want to make corrections to a moderated message before it is delivered to the subscribers. It is possible to do this using an extended form of the Approved line, using the following steps: * Obtain the original posted message, either from the CONSULT message that was sent to the moderator, or using the tokeninfo or tokeninfo-remind command: tokeninfo TOKEN tokeninfo-remind TOKEN * Edit the message and make the desired corrections. * Add an Approved line to the headers or the start of the body, with the following difference: after the password, put a comma and the token identifier: Approved: PASSWORD , TOKEN * Send the edited message to the address of the mailing list. When these steps are taken, two things will happen. First, the password will cause the moderation checks to be skipped. Second, when Majordomo sees the token identifier on the Approved line, it will reject the token. This will help to prevent another moderator from approving the delivery of the original posted message. The tokeninfo command displays information about a posted message, and the contents of the message, in the same block of text. The tokeninfo-remind command, in contrast, includes the posted message as an attachment. In some cases, the latter format may make editing and reposting a message easier; it depends upon the software that you use to read e-mail. Denying access -------------- In some cases, it may be necessary to discard posted messages from certain people automatically. There are several ways to accomplish this. The "postblock" flag, which normally causes messages to be moderated, can be used to discard messages. To enable this feature, add the following rule to the access_rules setting: post deny, reason="The postblock flag causes messages to be denied." $post_block Then, if you wish to deny all messages from non-subscribers, add "postblock" to the nonmember_flags configuration setting. To deny messages from a particular subscriber, use the set command to turn on the postblock flag for that subscriber: set LISTNAME postblock ADDRESS Another way to deny messages from a select group of people is to use an auxiliary list. In the access_rules setting, use the following rule: post deny, reason="Posted messages from this address have been banned." @banned Then, to deny posted messages from a particular address, use the following command: subscribe LISTNAME:banned ADDRESS If the "ackdeny" flag is set, the person whose message is denied will be sent a notice. If the "ack_attach_original" configuration setting includes the word "fail," the message that was denied will be attached to the reply. See "help set" and "help configset_ack_attach_original" for more details. Moderator groups (advanced topic) --------------------------------- Different groups of moderators can be assigned different moderation tasks. A moderator group is created by adding addresses to an auxiliary list with the subscribe command. The access_rules setting can then be adjusted to assign responsibilities to the new moderator group. For example, consider a list where one group of moderators is assigned to approve subscriptions and another is assigned to approve posted messages. All subscriptions and all posted messages are moderated. The addresses of the subscription moderators have been added to the "smods" auxiliary list, and the post moderators are in the "pmods" auxiliary list. The access_rules setting is changed: configset LISTNAME access_rules <<LPP post consult=(consult,1,pmods,), reason="All moderated messages require approval." ALL subscribe consult=(consult,1,smods,), reason="All subscriptions required approval." ALL LPP See "help configset_access_rules" for more information. Cookbook for common moderation problems --------------------------------------- Problem How do I allow only subscribers, and a select group of ------- non-subscribers, to post messages to the list? First approach: Subscribe all of the non-subscribers, but change their delivery class to "nomail" so they do not receive messages. subscribe-set LISTNAME nomail email@example.com Then, set the restrict_post configuration setting to allow only list members to post: configset LISTNAME restrict_post <<END LISTNAME END Second approach (most like Majordomo 1): Sign up the recipient users as usual, and put everyone else in a "posters" auxiliary list: subscribe LISTNAME:posters firstname.lastname@example.org then restrict posting to the main list and that sublist: Then, set the restrict_post configuration setting to allow only list members and members of the "posters" sublist to post: configset LISTNAME restrict_post <<END LISTNAME LISTNAME:posters END Problem How do I allow everyone in a certain domain to post, but ------- require approval for all other domains? Headers can be forged, so persistent people can easily bypass any restrictions based on the message headers. The following access rule will cause posted messages from any address outside the "example.com" domain to be moderated. configset LISTNAME access_rules <<END post consult, reason="Outsiders require approval." !/example\.com$/ END Problem How do I keep anyone, or a certain domain, from posting ------- while allowing all other users and domains to post freely? First note that headers can be forged and so if people really want to bypass a header-based restriction they can. Often what you REALLY want is to keep one user from posting while allowing everyone else to post, but the "freebie" domains make it easy to create new accounts and cause trouble. Here is how to lock out one domain, using Yahoo as an example. Note that the '@' and '.' characters need to be escaped with "\", and refer to "help patterns" for details on regular expressions: configset LISTNAME access_rules <<END post deny /\@yahoo\.com$/ END Here is how to lock out TWO domains, using Yahoo and MSN, and you can add more domains to the list as needed: configset LISTNAME access_rules <<END post deny /\@yahoo\.com$/ OR /\@msn\.com$/ END Here is how to lock out the entire Yahoo domain, and also any email address from any domain which contains the string "calliger": configset LISTNAME access_rules <<END post deny /\@yahoo\.com$/i OR /calliger/i END Problem How to I stop massive crossposting between my mailing list ------- and other mailing lists at this site, and perhaps other sites? You can do this using taboo_headers matches and an access rule. configset LISTNAME taboo_headers <<END /^(to|cc):.*some-list/i 10,crosspost /^(to|cc):.*some-other-list/i 10,crosspost /^(to|cc):.*another-related-list/i 10,crosspost /^(to|cc):.*yet-another-list/i 10,crosspost /^(to|cc):.*and-another/i 10,crosspost END These look like normal taboo_headers entries, with a twist: the information on the end contains a 'score' (or a 'severity') and a name. Taboo matches can be given names; when one of them matches, the score is added to that name. So for every match, ten points are added to the 'crosspost' match. Note that if you included your own list there, the match will start out at 10. Now, you have to test the score of the 'crosspost' match and do something with the message if it matches too many times. This is with an access rule: configset LISTNAME access_rules <<END post deny, reason="Cross-posting is prohibited" $taboo_crosspost >= 30 END The person who posted the message may or may not receive a notice indicating that the message was denied. See "help configset_nonmember_flags" and "help set" for details on the "ackdeny" setting. The "unique" delivery class can be used to keep people from receiving duplicates when messages are cross-posted to lists in the same domain. See "help set" for more details. Problem I want people to read my list for a few days before they post. ------- The number of days that have passed since the author of a message subscribed is recorded in the days_since_subscribe access variable. To moderate posted messages from people who have been subscribed less than three days, use the following access rule: configset LISTNAME access_rules <<END post consult, reason="New subscribers are moderated" $days_since_subscribe < 3 END If you don't find the answers to your questions here, please write to the software developers at email@example.com. Which settings take precedence? ------------------------------- Majordomo has many configuration settings which determine what happens to a posted message. You may wonder which settings have priority if one setting says a message should be sent to the moderators and another setting says a message should be thrown away. Majordomo takes the following steps to determine what rules apply to each message: * The access_rules setting takes priority. The first access rule with a "terminal" outcome (consult, deny, confirm, and so on) that matches the message causes that outcome to happen immediately. If no "terminal" access rule applies, only then can the other configuration settings have any effect, in the following order: * If the message exceeds a hard limit in the post_limits configuration setting, or contains an illegal body part according to the attachment_rules setting, the message is discarded. * Any of the conditions listed in the "Causes of moderation" section, earlier in this document, will cause the message to be moderated. * Finally, if none of these restrictions applies, the message is posted to the subscribers. See Also: help accept help admin help admin_commands help admin_config help admin_delivery help admin_documents help admin_monitor help admin_passwords help admin_subscribers help configdef help configset help configset_access_rules help configset_ack_attach_original help configset_attachment_rules help configset_default_flags help configset_moderators help configset_nonmember_flags help configset_post_limits help configset_whoami_owner help configshow help reject help set (for a description of the postblock personal setting) help showtokens help tokeninfo This is the "admin_moderate" help document for Majordomo 2, version 0.1201103110. For a list of all help documents, send the following command: help topics in the body of a message to firstname.lastname@example.org.
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