Dear John,

You're going to have to give me a few more clues. It was very nice of you to send me a Christmas card, but how am I supposed to know which John you are? Do you realise how many Johns there are in my long-tailed extended family? Are you my uncle John, my first cousin John, or one of the several second cousins of mine who bear that moniker?
You sent me a very pretty 'Aid to the Church in Need' Christmas card. Perhaps, therefore, you're one of the several clerical friends I have called John - I don't expect you to sign your Christmas card Msgr John, Canon John or Fr John, but maybe if you included even a partial address on the inside of the card, I could figure out which of you sent me this card.
Or perhaps you're a friend that I spent time studying or working with. The card bears the postcard of quite a large metropolitan area where I lived for a number of years. You are a unique individual, of course, but I must have a dozen or so friends and acquaintances from that city called John. Your handwriting is non-descript and I frankly can't decide which of my 'friends called John' is most likely to have sent me a card so promptly as to reach me in such good time.
So John, whoever you are... be assured that I would reciprocate your seasonal sentiments if I could figure out who you are, but I would appreciate it in future if you could provide even the tiniest hint concerning your identity so that I'm not reduced to dusting your card for fingerprints or DNA testing the postage stamp to establish who you might be.

Coridally yours,
(The one and only) Zadok the Roman