Pitfalls

• Prior to V8 sendmail, if the list of recipients contained an address that began with any of the prescanned switches, sendmail would wrongly view that recipient as a switch during its prescan phase. For example, mail to joe, bill, -Cool caused sendmail to try to use a file named ool as its configuration file.
• Command-line switches must precede recipient addresses. Switches that are mixed in with recipient names are treated as recipient addresses.
• Most versions of sendmail (including IDA and some versions of BSD but excluding SunOS and V8) syslog(3) a warning if the frozen configuration file doesn't exist. This can be annoying at sites that intentionally choose not to use a frozen configuration file.
• Prior to V8 sendmail, unknown command-line switches were silently ignored. Therefore sending mail from a shell script could fail for reasons that were difficult to find. For example, specifying the preliminary hop count wrongly with -j, instead of correctly with -h, caused your presetting of the hop count to be silently ignored.
• Some old BSD and SunOS versions of sendmail set the default sender's full name from the environmental variable NAME even when running as a daemon or when processing the queue. This can lead to the superuser's full name occasionally showing up wrongly as a sender's full name. IDA and V8 sendmail clear the full name in -bd and -q modes but use different methods. To prevent this problem under other versions of sendmail, the env(1) program can be used to clean up the environment passed to sendmail:
  
  

  % env - /usr/lib/sendmail -bd -q1h
  

  
  
  
• V8 sendmail uses getopt(3) to parse its command-line arguments so that a switch and its argument may have whitespace between them without harm:
  
  

  -C configfile
  

  But for bizarre historical reasons the -d switch differs. There may never be space between the -d and its arguments:

  -d 0.4
  

  If there is space between them, the argument (here, ) is taken to be a recipient name.