Cyrus and Netnews

Note that the NNTP support in Cyrus is still relatively young in the grand scheme of things, and has not been tested under a heavy Usenet load. That being said, the code appears to be stable and is currently running in production serving 50-60 newsgroups with a volume of about 6000 messages per day.

Introduction

Cyrus has the ability to export Usenet via IMAP and/or export shared IMAP mailboxes via NNTP. This is made possible by a new NNTP daemon which is included with Cyrus.

This document assumes that you have successfully been able to setup your Cyrus IMAP server. If you have not already done so, please refer to the rest of the documentation. This document also assumes that you are familiar with Usenet and shared IMAP mailboxes.

There is a diagram that shows the interactions of the various components of the NNTP support in Cyrus which may be helpful in understanding the "big picture".

Installation

You will need to build Cyrus IMAPd with the --enable-nntp configure option. This builds nntpd and the associated utilities.

Requirements

Obviously you must have a newsfeed or news reader access from your ISP or Usenet provider.

Configuration

The first thing that must be done is to decide where your newsgroup mailboxes will reside, either at the toplevel of your hierarchy (eg, comp.mail.imap) or rooted elsewhere (eg, netnews.comp.mail.imap). If your newsgroup mailboxes are not at the toplevel of your hierarchy, then you must specify the parent with the newsprefix in imapd.conf. Using the example above, newsprefix would be set to netnews.

You must create a mailbox for each newsgroup that you would like to receive/export before the newsgroups can be used. If some groups are private, be sure to set the ACLs accordingly. The tools/mknewsgroups script can be used to help facilitate mass creation of newsgroup mailboxes. When using this script, be sure to add posting rights for 'anyone' (eg. mknewsgroups -a 'anyone +p' ...) so that articles can be fed/posted.

Receiving articles

In order to receive usenet articles, you must make sure that the Cyrus nntpd service is enabled in cyrus.conf. The master/conf/normal.conf and master/conf/prefork.conf sample configs both include entries for nntpd (disabled by default).

Whenever nntpd receives an article, it automatically adds a To: header with email addresses corresponding to the newsgroups that the article is destined for (eg, post+comp.mail.imap). The presence of this header makes it easier for email clients to post/reply to the newsgroup. The "pseudo" user that is used when constructing the email address can be specified with the newspostuser option in imapd.conf (default = "post").

Push (traditional) feeds

If your usenet peer will be pushing articles to you, no further configuration is necessary, beyond letting your peer access your Cyrus server on port 119 (nntp).

Pull (suck) feeds

If you prefer to pull articles from your peer (and your provider allows it), then you can use the fetchnews utility which will retrieve articles from your peer and feed them to your Cyrus server. If supported by your peer, fetchnews will use the NEWNEWS command, otherwise it will fallback to keeping track of the high water mark of each group. You will probably want to configure fetchnews or suck as an EVENT in cyrus.conf to be called periodically (eg, once an hour, every 15 minutes, etc).

As an alternative to fetchnews, you can also use the suck program to pull articles from your peer.

imapfeed

Alternatively, if you already have an INN v2.3 server in-house you can use the included imapfeed utility (written by the authors of Cyrus) to feed articles to your Cyrus server via LMTP. Consult the INN documentation for further details.

Control Messages

Control messages are accepted, parsed and delivered to the corresponding control.* pseudo-group (eg, control.newgroup, control.cancel, etc) if it exists, so that they may be reviewed by an administrator.

Automatic execution of control messages is only performed if the newsmaster (default = "news") user has the proper access control for the given mailbox. For example, to allow cancel control messages to be performed for "misc.test" articles, give the "news" user the 'd' right on "misc.test". To allow newgroup, rmgroup and mvgroup control messages to be performed on the "misc" hierarchy, give the "news" user the 'c' right on "misc".

NOTE: No sender or PGP verification of control messages is currently implemented.

Reading/Posting articles

In order to have articles posted by your local users propagate to the outside world, you must specify the name of your usenet peer(s) with the newspeer option in imapd.conf. This is the host(s) that nntpd contacts to feed outgoing articles. Depending on the configuration of the newspeer option, articles will be fed to the upstream server(s) using either the POST or IHAVE command. Also note that you may specify an optional wildmat to filter which groups will be fed (see imapd.conf(5) for details).

Newsgroups can also be gatewayed to email by setting /vendor/cmu/cyrus-imapd/news2mail mailbox annotations to the corresponding email addresses.

News clients

If anonymous logins are disabled (default) in imapd.conf, then your news clients will have to be configured to login with a username and password, otherwise they will not be allowed to post. Furthermore, if plaintext logins are disabled in imapd.conf, then you might have to configure your news clients to use SSL/TLS and enable the nntps service in cyrus.conf.

If you want to allow your news clients to use the NNTP NEWNEWS command, you will have to enable the allownewnews option in imapd.conf.

Email clients

If you are exporting Usenet via IMAP, and your users' messaging clients are not savvy enough to reply to and post articles via NNTP, then you will have to configure your server so your users can reply to and post articles via SMTP.

To help faciliate this, you can set the newspostuser option to a userid which will be used to construct email delivery addresses for each incoming article. These addresses are inserted into a To: in the article. For example, if set to "post", an article posted to comp.mail.imap will have an address of "post+comp.mail.imap" inserted into the To: header. This will allow a user to easily reply to an article via email by using their messaging client's "Reply All" feature. Otherwise, the users will have to learn the correct email address format for posting and replying to articles.

In order for these email messages to be fed into your news server (and subsequently to the outside world) you need to use an email to news gateway, such as lmtp2nntp. You need to configure your MTA (Sendmail, Postfix, etc) so that lmtp2nntp is used as the local mailer whenever it receives a news article. A simple rule for doing this in Sendmail is shown below: 

# mail addressed to post+ goes to lmtp2nntp@localhost
LOCAL_RULE_0
Rpost + $+ < @ $=w . >		$#lmtp2nntp $@ localhost $: $1

For other configurations, consult the lmtp2nntp and documentation and your MTA documentation.

NOTE: If anonymous logins are disabled (default) in imapd.conf, then you should configure lmtp2nntp to use its "feed" operation mode.

Expiring articles

Expiration of articles is done by the cyr_expire utility. Control over when articles are expunged is accomplished with the /vendor/cmu/cyrus-imapd/expire mailbox annotation. This annotation sets the number of days that messages should be kept in the mailbox before they expire. All entries in the duplicate deliver database that correspond to these messages are also kept for the same number of days before they are purged (overriding the cyr_expire -E option).

Setting the expire time to 0 (zero) for a mailbox will ensure that neither the messages nor the corresponding database entries will ever be expired. This can be useful for shared mailboxes (e.g. mailing list archives) which are being exported via NNTP. Note that this will cause the duplicate delivery database to consistently grow in proportion to the number of messages in such mailboxes.

If a mailbox does not have an expire time set on it, then the messages will never be expunged, but the corresponding database entries WILL be expired after the default number of days (cyr_expire -E option).

Note that the /vendor/cmu/cyrus-imapd/expire mailbox annotation is inherited by child mailboxes, so that you may control expiration on an entire mailbox/newsgroup hierarchy simply by setting the annotation on the root of the hierarchy. For example, if you set the annotation on comp, then ALL of the newsgroups in the comp hierarchy will be expired at the same time. Similarly, if you set the annotation on alt.binaries, all of the binary newsgroups under alt will be expired at the same time (independently from comp).

last modified: $Date: 2004/02/23 22:56:13 $