How do you get someone to stop addressing things to your non-existent married name?

Over on Offbeat Home we're talking about how to politely correct people when they insist on addressing mail to your married name… even if you haven't actually changed your name. That's Offbeat Homie MonicaBerry's quandary:

My husband and I have been married for six years now and most of the family is fully aware of the fact that I kept my last name — actually, I'm sure my in-laws are well aware of this. But my mother-in-law keeps addressing mail and checks to me as if I had changed my name.

How do I address this issue in hopes of getting her to quit without being confrontational?

Those of you with experience or advice should join the conversation happening right now on Offbeat Home & Life.