When you write a letter to an embassy, it is very important that you appear respectful as well as knowledgeable about the subject in which you are writing. However, just as important is how you address the envelope and letter. This is the first thing the embassy will see. Therefore, it should be correct. There is certain protocol you are to follow when writing to an embassy. Not to mention the fact that you want it to actually arrive and not get sent back to you because it is incorrectly labelled.
Address the letter with one of the following: "Dear Mr./Madam Ambassador:" or "His/Her Excellency:" which is usually is not followed by their name, as it will be on the envelope.
End your letter with "Yours sincerely," with two spaces then your name, typed. In between these you should sign your name with a pen to make it look more professional.
Write the title and name in the centre of the envelope as "His/Her Excellency (First name and surname), Ambassador of (Country)." After the title, the next line should have the street address of the embassy. The third line should be the town, county or other principal subdivision. The fourth line, preferably in all upper case should be the country only, no zip codes or numbers. There should be no more than five lines, according to the U.S. Postal Service.
Write your name and return address on the top-left of the envelope as well as in the letter itself. Make sure you have the correct postage.
Follow standard address procedures if writing to an ambassador in your own country. For the United States, include the postcode.