Whenever this has occurred in my experience, the "other end" has used ...
• another email account with a different entry for my email address
• has numerous entries for my email address and selects one at random
• simply selected something like "Reply All" from someone else's email (address book)
Best bet — if this is truly annoying to you — is to let your e-correspondent know about same and have them fix their address book accordingly.
When I examine my various email accounts' address books (which collect sent and received email addresses of e-correspondents, I often find numerous entries for the same individuals; it's the fault of the email client you're using.
So, thanks. You've given me impetus to go through my various (collected) email addresses and delete the extraneous ones — which I'm going to do as soon as I post this.
