I'm wondering which are the main routes that letters surf? I mean, for exampe england to germany or spain to italy, and so on. It could be interesting to know that, I can choose vendors who ship from country and places that has less controls at the borders or that their letters come from a safe route (for example i guess that when a letter arrive to a big airport thare are less possibilites to pass controls), instead by trains it could be safer...
All mail in Europe is sent first to Germany for sorting and later shipped to Budapest where it is then flown via original wrights brother's plane to it's respective country. Source : Popular Mechanics June 2011