If you haven't mailed them yet, you're just out of luck. (Ok, you're not really out of luck - you have until Dec. 19 according to USPS, but are you actually going to get to them?) So here's an alternative. 

Facebook can't do it all, but dang is it ever close. They just added a new FREE feature that will allow you to create holiday cards and send them out. Seeing as it's a digital card, it's guaranteed to get there on time.

It's not just Christmas cards, they also have options for Hanukkah, Kwanzaa, and even Winter Solstice. The templates have a wide variety of interfaith and non-denominational options.

The feature started popping up on Facebook this week. You can send a digital greeting by clicking "send a holiday card" at the top of your news feed. From there you'll be able to choose your template, personalize it and then send.