> The reason was that people add lots of cruft to their email: 
> the repeated history 
> of replies and confidentiality notices that aren't germane to the issue.

Note that the citation and the signature can be stripped from the
email by roundup. There is a configuration option for stripping the 
citation if I remember correctly.
The problem with not responding to the tracker is that the stream
of exchanges goes beside the tracker, so it does not contain
the full set of records anymore.

> Perhaps another [mail] or [nosy] config option could be added to allow 
> the Reply-To to go to the author or roundup?

I agree with John that in the case that you do not want to receive emails,
you may want to set the sender to something like 
noreply@yoursite.example.com.

But another config options for explicitely setting the reply-to to
the author would be fine with me, if you really have the use case.

Best,
Bernhard