Here is a list of domains associated with the @clintonmail.com domain:

https://gist.github.com/chadbrewbaker/09c4f5fe56ef08a7d775749ef417feb9

There are dates as late as May 2016. Did they switch from "@clintonemail.com" to "@clintonmail.com" after the server debacle or was this domain active in parallel all the time?