I'd like to have an author-sorted index in addition to a date and a
thread index (3 indices). Is there a way to do this with the AUTHSORT
Yes, but you will also have to change a few other resources.
First, you need to set the OTHERINDEXES resource so an author index
will be created. Second, you need to change each index resource that
includes links to other alternate indexes (see LISTBEGIN and THEAD)
to include a link to the author index. Third, if you want a link to
the author index in messages, you will need to change the TOPLINKS
and BOTLINKS resources.
See the documentation of above listed resources for more information
and how to use them.