During about the time Mrs. Clinton was in office, I worked for a U.S. corporation supporting a U.S. government system where organizations interested in being government contractors were allowed to register. A notable fraction (don't remember exactly how many) of the contact e-mail addresses were "@aol.com", "@yahoo.com", etc.; and probably a few were "@retainedlawfirm.com", "@jointventure.com", "@parentsothersubsidiary.com", etc. I've seen the same pattern in WHOIS records for presumably legit organizations and in contact addresses on public-school websites.
As for me, from time to time I've had an "@outsourcingcompany.com" address as well as an "@clientcompany.com" address, and it's not always trivial to decide which address to use as the source for certain information, nor which of a similarly situated colleague's addresses to send it to (or to both for completeness).