Enable remote debugging debug with confENVDEF

The sendmail program allows the developer to turn on debugging and to print the queue from any remote site. This capability is useful for solving occasional problems but opens a potentially wide security hole.

In general, SMTPDEBUG should always be undefined. Later, when you become more expert with sendmail, you might want to have a standby version of sendmail ready (one with SMTPDEBUG defined), just in case you need it.

There is no debugging switch that will let you know whether a precompiled version of sendmail had this defined. Instead, you must run sendmail with -bs, then issue the SHOWQ SMTP command. If that command displays the mail queue, that precompiled sendmail was built with SMTPDEBUG defined, and so you should not use it!

    Part I: Build and Install
    Chapter 2. Build and Install sendmail
    Chapter 4. Configure sendmail.cf with m4
    Part II: Administration
    Part III: The Configuration File