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4.16. How do I prevent duplicate copies of email coming to the list

Occasionally I get the same email message coming to a list. Sometimes this is because people with broken MUAs (like Outlook) do a "group reply" and it puts the list address in twice, and sometimes it's a mail server hiccup. In order to prevent that, I run the mailing list through procmail as shown in the previous FAQ entry. Near the top of my procmail recipe file, I put the following code:

 :0 Whc: msgid.lock
 | formail -D 8192 /tmp/msgid.cache

 :0 a

The first bit keeps a message id cache of the last 8192 message ids received on the list, and the second bit deletes any messages whose message id matches one in the cache.

If you run more than one email list through the same procmail recipe file, be sure and use a different msgid.cache file for each list, possibly by calling it /tmp/msgid.cache.${MAILMAN} If you don't, people won't be able to send a message to two of your mailing lists at a time. That may be desirable to you.

Last changed on Fri Jan 25 00:22:17 2008 by jidanni

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