The sendmail program
offers the -d command-line switch, which allows
you to observe sendmail's inner
workings in detail. Understanding this switch can help you solve
complex email problems.
In earlier editions of this book, we attempted to document all the
debugging switches available, and provided a table showing which were
useful. For this edition, however, we will limit our detailed
description to V8.12 sendmail and only to those
debugging switches considered useful. This was done because debugging
switches show the inner-workings of sendmail,
and, thus, those that are other than
"useful" can change dramatically
from release to release and are impossible to accurately represent in
a static book.