Return To Sender

I received a Christmas card from someone I've lost touch with in recent years, wanting to catch up over coffee. I would like to, however, they did not put their return address on the card or the envelope!

I only hope that the mobile phone number I have for them is still valid!

Did this person not learn how to address and write a letter when they were at school? Maybe I am showing my age a bit here, but I was taught when you send a letter or a card, you should always have the senders (your) address on the back of the envelope.