Send from one address only

I have two email accounts set up on mac mail. However, I only ever want to send from one of these addresses. Mac offers me two options to send from despite my having selected to set from one account only in smtp settings. Whats more, Mail by default gives me the address I DONT want.

Open Mail - Preferences - Composing tab - Send new messages from:
and select the account you want.

But even with that set, you need to make sure that Mail follows that default. If, for example, you respond to an email, it will send from the address the original was sent to, not the default bobtomay indicated to set. And sometimes it "sticks" on that return address for the next email, too. Bottom line: Check each time.