I am going to have to describe this in layman's terms so apologies in advance.

When you write an email in Mail, as you start typing the person's name the system drops down a list of possible email addresses. Likewise when one of those people writes to you, it shows as 'Colin Smith' not smith%909@gmailwhizz.com or whatever.

My system has somehow managed to confuse me with another person, so email addressed to one of my addresses shows the wrong name in the header. The email address is correct, it just shows as 'Jane Smith' instead of 'John Brown' if you see what I mean.

Is there a way to correct that?