Mail comes in under different name

I'm using Mail on my MacBook Pro (10.6.8) and it's misbehaving. My email comes in - I'm getting everything I'm supposed to be getting - but in the "to" line, it has a different name. It is addressed to someone I had a brief email correspondence with about a week ago. Everything else is fine. How can I clean this up? Or can I?

Any advice would be muchly appreciated.