Reply to "Merry Christmas and a happy new year"

When I have opened my email inbox, I found I received a greeting of ""Merry Christmas and a happy new year" from a friend of mine on December23. Today is Dec 27, can I still say "Merry Christmas and a happy new year" to reply this email?

I think "You too" is best. Your could also say "Same to you", a little more old-fashioned in my opinion. Depending on the date and other context you might also say just "Merry Xmas" or just "Happy New Year."

Yes, or you can say "Thank you - Sorry I didn't get back to you in time to wish you a Merry Christmas, but not too late to wish you a happy new year as well."

I consider "Merry Christmas" fine for a few days after, though.

Christmas (at least in the Church) is a season that begins on Dec 25. The "Twelve Days of Christmas" is the period from Christmas Day to Epiphany (Jan 6).

So, yes, you can still wish someone Merry Christmas on Dec 27.

Outside of the religious side of things, I would find it odd to be wished "Merry/Happy Christmas" after December 25th. If I received that email on December 27th, I would reply with "Thanks. I had a great Christmas and I hope you did too. Enjoy your New Year" or something similar.

How about I hope you had a good Christmas?