(via stephan.paukner.cc)
Whenever sendmail has to deliver mails to other hosts which cannot be reached at that time, the messages are kept in the queue. Although the other hosts could be reached again and you want to tell sendmail to flush the mail queue, the command
sendmail -q -v
does not really try to reconnect to these hosts and still assumes that the connection timed out. The reason is that the hoststatus is cached, per default for a period of 30 minutes. Using
sendmail -OTimeout.hoststatus=0m -q -v
you can re-run the mail queue and force sendmail to reconnect to the hosts.
