Now I don't mind receiving a card address to Mr and Mrs (dp inital) on envelope. That is correct etiquette imo.
What really bugs me is when a card is given to me by a friend or neighbour who knows me better than dh and it is addressed to and from dh's name 1st.
Ori s this correct etiquette too. If I write a card I always sign my name 1st and if I know the female part of couple more I address it to her 1st.