Sendmail, 3rd Edition

Pitfalls

• The use of the # to place comments into a .mc file for eventual transfer to your configuration file might not work as expected. The # is not special to the m4 processor, so m4 continues to process a line even though that line is intended to be a comment. So, instead of:

  # Here we define $m as our domain

  (which would see define as an m4 keyword), use single quotes to insulate all such comments from m4 interpretation:

  # `Here we define $m as our domain'

• Never blindly overwrite your sendmail.cf file with a new one. Always compare the new version to the old first:

  % diff /etc/mail/sendmail.cf oursite.cf
  19c19
  < ##### built by [e-mail] on Sat Jan 1  11:26:39 PDT 2000
  ---
  > ##### built by [e-mail] on Fri Dec 13 04:14:25 PDT
  2002

  Here, the only change was the date the files were built, but if you had expected some other change, this would tell you the change had failed.

• Never edit your sendmail.cf file directly. If you do, you will never be able to generate a duplicate or update from your mc file. This is an especially serious problem when upgrading from one release of sendmail to a newer release. Should you make this mistake, reread the appropriate sections in this book and the documentation supplied with the sendmail source.

• Don’t assume UUCP support and UUCP relaying are turned off by default. Always use the nouucp feature (FEATURE(nouucp)) to disable UUCP unless you actually support UUCP:

  FEATURE(`nouucp')           ← recommended through V8.9
  FEATURE(`nouucp',`reject')←