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sendmail Milter

Posted on 2002-05-13
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Last Modified: 2013-12-17
Dear experts

I have installed sendmail 8.12.3 on Sun 8 system. It seems to be fine in the sending functions.

Does any know any the email blocking ? As far as I learn that the Milter function in sendmail can do the email blocking.

Please advise the setup / configuration changes in 8.12.3 ? e.g sendmail.cf or m4 etc.

Thanks in advance

Edmund
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Question by:edmundli
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6 Comments
 
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Expert Comment

by:jlevie
ID: 7007661
The libmilter support in sendmail is merely a mechanism for hooking external filters into sendmail without requiring a modification to sendmail. Basically libmilter defines a communication mechanism and API for attaching a filter to an existing sendmail installation. There are quite a few libmilter filters available and you can find links to a number of them via http://www.milter.org/.
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Author Comment

by:edmundli
ID: 7008226
I have a look of this before.

Can you send give some steps in order to make the milder works ?

e.g. mc or sendmail.cf changes

Edmund
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Author Comment

by:edmundli
ID: 7049519
Hello,

Any feedback ?
Edmund
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Accepted Solution

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jlevie earned 100 total points
ID: 7049606
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To have a sendmail that includes libmilter support you need to be using sendmail 8.12.3 (which you are) and have:

APPENDDEF(`conf_sendmail_ENVDEF', `-DMILTER')

in your sendmail-8.12.3/devtools/Site/site.config.m4 file. Then build sendmail in the usual manner. The libmilter interface is then built with:

> cd sendmail-8.12.3/libmilter
> ./Build
# ./Build install

You'll usually need a number of the header files and perhaps some of the libs from the build of sendmail available. I also find that it's nice to have the cf hierarchy available outside of the sendmail sources and that can be done with:

> cd sendmail-8.12.3
# cp -r cf /usr/share/sendmail-cf
# mkdir -p /usr/local/include/sendmail
# cp -r include/* sendmail/*.h /usr/local/include/sendmail
# mkdir -p /usr/local/lib
# cp obj.???/*/*.a /usr/local/lib

replacing obj.??? with the directory that the build of sendmail produced.

Another email virus filter system that can use spamassassin for spam filtering that looks really good to me (and happens not to use libmilter) is MailScanner (http://www.sng.ecs.soton.ac.uk/mailscanner/index.html). In some ways I think it might be preferrable to a libmilter approach in that it's behaviour if the filter has problems is more to my liking.

The problem with a libmilter approach is what happens if the filter package chokes. One approach is to simply pass the mail through unfiltered, which is what the good filters do. That's probably fine if all you are doing is spam checking. But if you are also doing virus filtering it would be better to have the mail queued up until the filter can be restarted or fixed, whatever. The MailScanner approach is nice because it places incomming mail in one queue and the filter moves it to a delivery queue. If something happens to the filter the mail is still in the input put and can be processed later.
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