You should always use the official postal service in Lanzarote to send letters and postcards.
We’ve been contacted by a couple of readers who used “non-official” postage stamps that they bought from tourist shops in the resorts and then put onto postcards to send home. In both cases, they were told by the shops to pop the postcards into letter boxes outside the shops. The postcards never arrived.
One of them remembered the stamps were issued by a company called “Sun Post” and we’ve found threads on Trip Advisor where other people have bought stamps from them and where once again, the postcard were never delivered.
We’d advise going to a Correos Post Office, they are all over the island, but here are the addresses of the ones in resorts:
Puerto del Carmen
Calle Mungia 2 – right next to the Biosfera shopping centre
Centro Commercial Las Maretas, Avenida de las Islas Canarias – opposite Superdino supermarket
Calle Correillo – two streets back from the sea front in the middle of town
If you go into any of those you can buy stamps and they will even take your postcards from you to send them. You should only ever post letters and postcards in the official Correos post boxes, which are yellow.