Actions by sending signal

SIGHUP
	Send QUIT immediately for all open SMTP connections to terminate
	delivery, and after termination of all SMTP sessions (timeout
	included), make response for LMTP session correctly (smtpfeed
	will exit with EX_OK). On LMTP response, TEMPFAIL will be
	returned for unprocessed recipients at the moment.

SIGINT
	Internal state information will be dumped.

SIGTERM
	Close SMTP connections immediately (without sending QUIT command
	nor timeout processing), make response for LMTP session correctly
	(smtpfeed will exit with EX_OK). On LMTP response, TEMPFAIL will
	be returned for unprocessed recipients at the moment.

SIGQUIT
	Close SMTP connections and LMTP connection, and smtp will exit
	with EX_TEMPFAIL. Delivery for the message will be retried for
	all recipients 	even if some the message has been sent to some
	recipients. (Some recipients will receive the same message twice).
