Innocent mistake or bold scam?

I received a letter with the following envelope information:

FROM:
MFS MUTUAL FUND SETTLEMENT
In re Mutual Funds Investment Litigation
c/o The Garden City Group, Inc.
P.O. Box 9410
Dublin, OH 43017-4510

TO:
MFS HERITAGE TRUST CO TRUSTEE
IRA A/C RICHARD R DUFFIELD
(my street address here)
(my city, state, and zip here)

The letter is not addressed to me so I did not open it.  But  I am the first home owner at my address and the house was built to my specifications a few years ago.  So I know that a Richard Duffield could never have had this address.

It could have been a mistake in the address, but I suspect it's an attempt at fraud by pretending an administrative mistake and  luring someone into paying fees to receive someone else's settlement. Once the victim takes the bait the scammer can also blackmail them because technically the victim also committed a crime by opening mail addressed to someone else.

I didn't open the envelope. I marked it "not at this address" and put it back in my mailbox for the postman to pick up. I think that's the right thing to do when receiving mail addressed to someone else who I don't know.