A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 102,617
The email talks about responding to the email. I hope they don't expect OP to give credit card details by email.
Has the OP checked that the email did indeed come from the hotel?
I wonder whether calling Marriott would be a way to make the deposit without calling or emailing the hotel.