Did anybody else receive deposit mails when booking Protea hotels? Where they marked as phishing and what did you do about that?

The full story:
Made a booking (through Marriott.com) for the Protea Hotel Kruger Gate.
The booking can be cancelled for no fee until the day of the stay, my credit card is on file as a guarantee. No deposit is mentioned or taken when I made the booking.

A few hours later I receive a mail from reservations-at)proteahotel-dot)com.
This mail is marked as a phishing mail by Gmail. It seems legit though as it mentions the name of the hotel, the date of the stay and the number of nights. The deposit amount is almost the complete amount for the stay (a few dollars off)

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I find it a bit odd to receive this mail as nothing about a deposit was mentioned on the Marriott site. It makes me wonder if the booking is truly fully flexible, never had to pay a deposit with Marriott before on these types of bookings.

If I get a refund of the deposit when I cancel I don't mind paying the deposit but as the mail is marked as phishing every time (I received a reminder mail with the same problem) Gmail removes the link to pay the deposit. So I can't pay, even if I would like to.

Can they cancel a confirmed reservation if you don't pay the deposit?

UPDATE: I tried replying to the reservations mail but nobody seems to monitor that address. I reached out to Marriott Customer Care through Marriott.com.