I have received seasons greetings and electronic Christmas cards from people I don't know. I'm grateful yet geewhiz What a waste!
Before you send anything via any method think first about the relationship you have and build on that. If you don't yet have a relationship sending a Christmas card won't help build one.
I have also received numerous emails recently from people I can't vouch for and people I do know who haven't been in touch this year asking for recommendations. Give, Give, Give, then Ask which is the great reminder of Gary Vaynerchuk's most recent book.
Be the difference you want to see in the world.