APLawrence.com -  Resources for Unix and Linux Systems, Bloggers and the self-employed
RSS Feeds RSS Feeds











(OLDER) <- More Stuff -> (NEWER) (NEWEST)
Printer Friendly Version
->
-> Review of Sendmail Milters by Bryan Costales and Marcia Flynt


Sendmail Milters




libmilter is a sendmail library for mail scanning by external programs. You can check to see whether your sendmail supports it with:

sendmail -d0 < /dev/null | grep MILTER

Sendmail 8.13 hase MILTER enabled by default.

With libmilter, sendmail can call other programs to help determine the disposition of a message. There can be multiple external programs, and sendmail makes calls at different points: when a sending machine connects, when it sends its HELO greeting, when it sends MAILFROM:, etc.

The milter itself can be written in any language: there are Perl milters, Python milters and more. The milter itself tells sendmail what parts of the process it wants to be involved in. It can accept (which means sendmail won't contact it again for that particular message), reject in various ways (which causes sendmail to reject or discard the message right then), or simply delay its decision until later in the process (which means that sendmail will send it more information that it has requested to be notified of). Multiple milters can process the same information; sendmail will call each unless and until one tells it to reject the message.

Everything you need to know about writing milters is here. I was a little amused that the authors gave advice on attracting spam in order to test a milter setup: I don't think too many of us need to worry about not having enough spam to test with.

Milters can be written in any language, but do require C hooks to interface with sendmail. As this book shows C code, you'll need at least read-only capability with C to get a lot out of it. However, it is also an excellent overview of spam in general, the techniques used and proposed for blocking, and how the spammers get around our efforts. I found that section of the book very interesting and learned a bit, too. There's fairly deep coverage here; even covering details like decoding mime.

If you are a C programmer (or can at least read it well enough to translate the concepts to other languages) interested in adding milters to sendmail, this is necessary reading.

  • Bryan Costales and Marcia Flynt
  • Addison-Wesley
  • 0321213335

Amazon Order (or just read more about) Sendmail Milters  from Amazon.com



If this page was useful to you, please help others find it:  





Comments?




More Articles by - Find me on Google+



Click here to add your comments
- no registration needed!


Don't miss responses! Subscribe to Comments by RSS or by Email

Click here to add your comments


If you want a picture to show with your comment, go get a Gravatar

Kerio Connect Mailserver

Kerio Samepage

Kerio Control Firewall

Have you tried Searching this site?

Unix/Linux/Mac OS X support by phone, email or on-site: Support Rates

This is a Unix/Linux resource website. It contains technical articles about Unix, Linux and general computing related subjects, opinion, news, help files, how-to's, tutorials and more. We appreciate comments and article submissions.

Publishing your articles here

Jump to Comments



Many of the products and books I review are things I purchased for my own use. Some were given to me specifically for the purpose of reviewing them. I resell or can earn commissions from the sale of some of these items. Links within these pages may be affiliate links that pay me for referring you to them. That's mostly insignificant amounts of money; whenever it is not I have made my relationship plain. I also may own stock in companies mentioned here. If you have any question, please do feel free to contact me.

I am a Kerio reseller. Articles here related to Kerio products reflect my honest opinion, but I do have an obvious interest in selling those products also.

Specific links that take you to pages that allow you to purchase the item I reviewed are very likely to pay me a commission. Many of the books I review were given to me by the publishers specifically for the purpose of writing a review. These gifts and referral fees do not affect my opinions; I often give bad reviews anyway.

We use Google third-party advertising companies to serve ads when you visit our website. These companies may use information (not including your name, address, email address, or telephone number) about your visits to this and other websites in order to provide advertisements about goods and services of interest to you. If you would like more information about this practice and to know your choices about not having this information used by these companies, click here.

pavatar.jpg

This post tagged:

       - Mail
       - Security
       - Sendmail















My Troubleshooting E-Book will show you how to solve tough problems on Linux and Unix systems!


book graphic unix and linux troubleshooting guide



Buy Kerio from a dealer
who knows tech:
I sell and support

Kerio Connect Mail server, Control, Workspace and Operator licenses and subscription renewals



Click and enter your name and phone number to call me about Kerio® products right now (Flash required)