That is one way of re-using postcards.
The other is, if you happen to love postcards like me and Silvia, is to experience someone sending postcards you know of again. This is more or less what exactly happened:
Silvia: Ian, send me a postcard!
Ian: I can send you the empty cards at home I will never use and re-post the postcard Jana sent me!
[I might have sent a postcard with a not so uplifting Polish alcohol reference once. Ian is split between being offended and pleased and takes the opportunity to remind me.]
Me (with a happy voice): Ian, it made me think of you!
[It did. And it actually was a kind precaution.]
(The postcard above was sent to Misa. It made me think of her.)