Praise then darkness, and creation unfinished

I'm using the default MacOS Mail program. Recently, I've been noticing that some of my email is showing up with the correct email address, but address to someone else. A specific someone else, and I have no idea how her name got into my program's configuration. (Yes, I have sent her email from this machine, but I've sent lots of people email.) And I can't find how to change it back; the "how to set up your email" pages I found quickly assume you don't already have it set up, or that you want to add a new account, not that I am Redbird and my outgoing mail identifies me correctly, but the system is displaying a friend's name as the recipient of my mail. (The most recent was from the Madison Concourse Hotel, warning me that if I want to cancel my room for Wiscon I need to do it soon. That one has my correct name in the HTML message, so I know they know who I am, but my friend's name in the header. (I am eliding my friend's name and even handle out of what may be an excess of caution.)

Suggestions would be welcome, either how to fix it or even guesses as to what may have happened here.

ETA: Resolved, the problem was in the address book, where I'd pasted the wrong email address into my friend's entry.