Why bother with conventional postcards? Why not send a postcard by email with the help of a wonderful little known website called losgigantes.com.
Before you set off on your holiday, take with you the email addresses of your family and friends.
When in Los Gigantes, go to an Internet Cafe (not sure if losgigantes.com still have such a facility).
Go to the Home Page of losgigantes.com and click “Useful Information”. Click on “Send a Postcard.” You will be presented with a list of categories. Select a photograph from your chosen category – say, Los Gigantes, and follow the instructions. You can enter a message to your intended recipient and even upload your own photograph from say, a usb memory stick or your camera card. Your photo can be up to 5 Mb.
I've just given it a try and it works perfectly. Why wait for 5 weeks for your postcard to be delivered through the normal post when it can be delivered instantly by email ?
Here's one I sent earlier-