Sendmail Theory and Practice - Avolio and Vixie

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Although some reviewers have seen this as an introductory book, and have advised reading it prior to the "Bat" book, I think most folks would find that really difficult. In fact, you probably need a fair amount of prior knowledge before diving into this book. I'd therefor only recommend it as a companion for other resources. As that, this is useful because it does contain examples and suggestions that vary from the "Bat" book, and that always helps understanding.

This is a 1995 edition; obviously some of the material is out of date. A fair amount of attention is given to UUCP subjects, which few people use for mail anymore (of course, if you do, you'll be very happy to find this coverage!). It doesn't cover spam at all, and its entire concern with security is avoiding expansion of aliases. On the plus side, there are good examples of troubleshooting and in general the explanations and examples are well chosen and well done.