Yes, the same happens for me, but I also have all the historical entries. e.g. I have an Apple id myname@me.com and in the dropdown there is myname@me.co @mac.com and @icloud.com. But also a dozen other mailboxes that I don't even have an entry for in my malboxes (although they are all current valid email addresses I own). It's not just academic. Some of them appear to be mislabelled and I sent an email earlier today to a financial organisation that was insisiting it came from one particular address of mine and it went from one of my other addresses. It's a right mess and I would dearly love to tidy it up.
if an outdated email address pops up, i go into mail>window>previous recipients. type in name in search. you can delete unwanted addresses. but if an address is still in contacts edit that out.
I know all about the previous recipients feature which I use frequently but I am not talking about remembered recipients, I'm talking about email accounts.
Thank you. I have posted this on several forums but you are the first person to mention aliases. I have done some tidying as a result, still not completely tidy but a lot better.