I should add that you can also choose Users –> Export to CSV and get a spreadsheet of all user information, including their email addresses. From there you could put the addresses into an email program, though I’ve found it’s best to do it in batches of 30 or so.
I suspect there might be a plugin conflict or a server setting that is preventing you from accessing that feature, Lisa. It might take me awhile to resolve, if at all. En attendant, my test user (which is an admin on the http://ucincinnati2017.thatcamp.org/ like you) DOES have the Users –> Export to CSV option, so I’ll ask you to use that for now. If I get the Email Users plugin thing resolved I’ll let you know.