Receiving mail in ex's name to husbands home address

Not sure if this can be answered on this forum: My husband is receiving bills for his son’s medical bills to his address but the catch is – it is addressed to the ex wife at his address. She is trying to send the bills to him but they are being address to her at his address. They have been divorced for over 12 years now…she don’t have the guts to hand them to him directly and is trying to have them sent to him via the mail. The last time I check it was against the law to open someone mail. Am I correct in returning it to the sender and letting them know that the address is incorrect for the addressee. We have no problem with help paying the bills but it is the way she going about it makes it illegal I believe by having the bills address to her at our address.

You may return the bills to sender.

thanks for the quick response. I will drop back in the mail.