At the regional post office in Murcia, in south east Spain, I asked for stamps to Europe. It was all very clear and one guy even spoke English: one such stamp for up to 50 grams heavy letters. I bought ten of them and put such a stamp on a 40 gram letter to Linköping, Sweden, and it made it all the way to my friend's mailbox smoothly. But, the next time I came to the post office, they said that in fact I needed two such stamps for a letter of more than 20 grams within Europe. Same stamp is valid for letters up to 50 grams WITHIN Spain but for 20 grams outside of Spain. Ok, now convinced I knew it all, I put one such stamp on a postcard à 0,005 kg and went to the biggest post office in Madrid. THREE people were needed to help me modify my postcard stamp and getting the right three special stamps, worth 25 cents in total, in addition to two heavy-letters-within-Spain stamps.
"Do you still like post office?" friend says with a smirk.
"Take a photo of my frustration", I reply.