My problem has been solved. Briefly:
> The problem I'm having is that I'm able to issue commands
> locally i.e. from the machine on which it is installed,
> but if I send commands remotely they simply go into the
> mail spool and I never get any response.
The solution was to restart sendmail. I presumed, since
local requests were being processed, that sendmail had been
restarted, but this turned out to be wrong. Jesse Brown
provided a possible explanation:
"I would say it is because when you started another instance
of sendmail to deliver it locally it read in the config file
and did it's thing, but the instance on port 25 handn't been
restarted, and so was reading off an old copy of the config
file it had read into memory.. :)"
Anyway, thanks to all of you who helped. I hope my posting the
solution here helps someone in the future.