I agree with Comilao that a normal greeting is "Greetings from...". However you don't have to be traveling and actually this greeting works perfectly for sending your first postcard to a foreigner since you're saying hello on behalf of yourself and your city/country. Other greetings for future postcards can be very casual, postcards are casual in nature, so things like "Hey how are you?" "It was nice hearing from you." "I hope you receive this well" (a little more formal) "How are things in (insert city or country or state or etc)" Does this make sense? Good luck!

Firstly, normally people send postcards while travelling. So the I normally write it with "Greetings from (the place where you send the postcards)" It is fine to write a postcard in this way, because postcards are not like formal letters.

Be careful of your words - "politically" and "politely" have completely different meanings. Same goes for "accommodation" and "recommendation". http://www.thefreedictionary.com/ I agree with the other members: "Greetings from ____" or "Hello/Hi from ____" are typical opening phrases for a postcard.

And on the subject of politeness - please be aware that people may take offence if you refer to them as 'foreigners'.