The -v command-line switch tells sendmail to run in verbose mode. In that mode, sendmail prints a blow-by-blow description of all the steps it takes in delivering a mail message.

After the sendmail.cf file is parsed and after the command-line arguments have been processed, sendmail checks to see whether it is in verbose mode. If it is, it sets the HoldExpensive option (HoldExpensive) to false and sets the DeliveryMode option (DeliveryMode) to interactive.

The -v switch is most useful for watching SMTP mail being sent and for producing expanded output when viewing the queue.