This was on the news. It is legit. The mortgage companies do not want to pay the $5 service fee. By having the original they can mail it in and there is no charge. But they are obligated to pay. SO even if you do not send it to them, they will have to pay it. There is another thread about this already.
Thanks for the heads up, I've not gotten a letter about it yet, but DID receive the tax bills from cook county assessor's office. Since everything is paid in escrow, I keep the bill, they pay the tax for me. But, if that letter does come, I'll make a copy of my tax bill and then send it along.