Pitfalls

• It is best to debug sendmail in a window environment, within script(1), with emacs(1), or something similar. Debugging output can run to many screens.
• Activities of the daemon can be observed only if the -d99.100 debugging switch is combined with the others selected. This switch prevents the daemon from disconnecting from the controlling terminal. Without this switch, sendmail silently discards its debugging output.
• Sometimes debugging output seems not to be printed:
  
  

  % /usr/lib/sendmail -d11.1 you < /dev/null %
  

  When this happens, add the -v command line switch to keep the output attached to your screen:

  % /usr/lib/sendmail -v -d11.1 you < /dev/null many lines of output here %
  

  
  
  
• There must be no space between the -d and its numeric arguments. If you put space there, the numeric arguments may be interpreted as recipient addresses.