I am in Spain on holiday right now and have a question because I saw a post box where it said at the top „Only official stamps allowed“. Now I am wondering what an unofficial stamp could be? I bought mine at a touristy shop that also sold postcards and other stuff and they look like this:
As long as the stamps say Correos Espana (=Spanish Post), you are safe - 99% sure on this
There are (were?) some private postal companies with their own stamps, which were often sold to tourists (a bit similar to Universal Mail in the UK) and cards with these stamps would not be forwarded by Spanish Post, I think, since they would have zero postage from their point of view.
Thank you so much!!
Your stamps are officials, yes 
In Spain the official post boxes are yellow and they have this logo
As @delenn_mir say, there are private companies with own stamps and they can’t use in Correos post boxes.
My English is not good, I hope you understand me 
Muchas gracias! Now I understand!
Just a kind tip (if you don’t know it yet):
“tarifa B” stamps must only be used on postcards sent to Europe including Greenland but excluding Albania, Armenia, Bosnia, Cyprus, Georgia, Malta, Moldavia, Russia (yeah, strange country division from the Spanish Post…)
“tarifa C” stamps must be used for all other countries not included in “tarifa B” and “tarifa D”
“tarifa D” stamps must be used for Australia, Canada, USA, Japan, New Zealand and Russia
Thanks so much for the tip!
