Certain embassies in Tehran (notably the Chinese, but also the Tajiks, and in certain cases, the Uzbeks as well) require a letter from your embassy that states they have no objections to you going to their country. That is an extra hassle as some embassies are not so happy to do that for you and wish to charge you for it. I decided to collect the information pertaining to each country here. Updates posted in this forum topic.
If you don’t have an embassy in Iran, check which embassy would be responsible for your nationality. If you are an EU citizen without embassy in Tehran, you can get it from any other EU embassy.
Austria: 40 euros, on the spot, to be paid in euro.
Belgium: Free, send a mail and pick-up next day (July 2016)
Bulgaria: Easy and free (May 2015).
Czech Republic: Pick-up next day, free of charge.
Denmark: Easy, but now costs 30 Euro (April 2016). If you are not Danish, contact them in advance to avoid discussion.
France: Letter requested on Thursday collected on Sunday. Initially supposed to be collected on Monday but i insisted a bit to have it faster. Free.
Germany: 25 euro, on the spot, to be paid in rial. Come in the morning.
Poland: free, possible to make at the Polish embassy the same day (July 2015)
June 2016: You have to make an appointment, otherwise they will not allow you in. Busy embassy. Had to wait for an hour despite having an early appointment at 7.30 AM and once I went in they said making the letters of No Objection would take another 3 hours. I said the other embassies would be closed then and got it within 10 minutes. Paid 2x 30 euro’s.
February 2016: 15 minutes, 30 euros. Only serves Dutch nationals.
South Africa: I got the required letter from your embassy from the South African embassy on the same day in Tehran and they were very efficient and issued it 20 minutes. (December 2015).
Spain: Only for China, not for Uzbekistan (May 2017). After sending a mail, pick-up next day. Free of charge (July 2016)
Before: one says it was easy to get (December 2014), the other says it was difficult (May 2015) because the embassy wanted to see flight reservations – overlanding not supported by the Spanish burócratas?!