The last few suggestions are fine if you're wanting to create throwaway email addresses, but does not help the idiots who don't know their own email address and use your genuine/master one. In my case I have a firstnamelastname@gmail.com address that a truck/RV sales company in Boise, Idaho keeps handing out to people instead of their own which is firstnamelastnametravel@gmail.com.
They have their own .com domain registered and in use for their web site, so why they insist on using a Gmail address I have no idea. I've complained to them a number of times, for which they have apologised. Still keeps happening periodically though... 😡