sendmail, 4th Edition

The regex Library

The powerful rules in the sendmail configuration file are a good defense against spam. One method of making these rules more flexible is to add the ability to use regular expressions with the regex library. Use of the regex library is covered in regex on page 932.

If your operating system currently lacks regular expression support, you can search for a replacement on the Web. If you install your own regular expression library, avoid including the file regex.h from your standard /usr/include. If you do, sendmail will likely fail and dump core. Instead, be sure to include the regex.h from the distribution you downloaded.