At my first firm gig, there were 3 of us who hung out a lot. Two of them I keep in contact with and are on my Christmas card list. The other one I haven't talked to since going in-house 8 years ago but we end up exchanging Christmas cards. I know he and one of the other two get together on occasion.
Quite frankly, but for him feeling "left out" from the Christmas card list in case one of the other two talk to him about it, I wouldn't send one. We really don't talk at all aside from the Christmas card niceties and don't see us talking in the future. We weren't that close, as he was always closer with the other two. Then again, it's a stamp. WWYD?

DD -- 5YO
DS -- 3YO
Re: Christmas card WWYD
I'm a less is more gal- especially in the Christmas Card arena- I'd say it's ok to not to send one.