Leib Moscovitz wrote:

Don't know how well suited this would be for your needs, but X1 Search
can be used for various types of email searches - might be worth giving
it a try.

+1 on X1 Search.

Another option could be dtSearch (dtsearch.com) What's neat about it? You can set it to return results synonymous with your term, set 'fuzzy' parameters, etc.. This can help uncover concepts.

And--- a 3rd option -- noggle search (noggle.online) It makes use of Carrot2 (carrot2.org) clustering.