I looked at the CEX.IO website and couldn't find any doge or namecoin markets. Are you sure it was CEX.IO that sent the email? The only CEX.IO markets I could find were for bitcoin, ethereum, and litecoin, but I have never registered on it so I might have missed some.
Yes it was from them. There was a time when I mined on ghash.io (owned by cex.io) and you could sell merged mined coins like doge and namecoin directly on the exchange. Haven't visited in years; but, still receive emails.