After a longer time I’ve again updated Recent Menu, available on the Mac App Store and as a trial download on this website. Version 1.2 contains a new feature allowing it to exclude specific file names (or parts of it) or file types from being shown in the search results. You can do this by using the negation operator ! in any search string.
For example, to exclude email messages from being shown in the search results, you could have a filename custom search and use ‘!*.emlx’ as search string. The same result is reached by having a UTI custom search and using ‘!public.message’ as search string. This should work without any problems. If you experience trouble, though, please drop me a line.