Did the email include identifying information about your account, or was it non-personalized, and simply sent to your email address?

If the latter, is it an email address that someone else might pick as a throwaway, like [email protected] (common name plus common mail service)?

If so, it might be something benign--I'm constantly getting legit notices about legit accounts I never created at my gmail address (myfirstnamemylastname), and my name isn't all THAT common. It may be that someone used your address to sign up for their own MP account.

Of course, you are still wise to check.