The sendmail program
-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.