When writing a letter to a U.S. ambassador who is currently serving at an embassy overseas, open the letter with the salutation "Dear Mr. Ambassador" or "Dear Madam Ambassador." Keep the tone of the letter formal, and write clearly and professionally.
The first line of the mailing address for a letter to a U.S. ambassador should begin with the words "The Honorable" and then the ambassador's full name. The second line should say "Ambassador of the United States," and the third line should say "American Embassy." The mailing address should follow on subsequent lines.
If the letter is being sent to a non-U.S. ambassador, the "Dear Mr. Ambassador" or "Dear Madam Ambassador" salutation is still appropriate; the salutation "Excellency" can also be used for less formal correspondence. The first line of the mailing address should begin with the words "His Excellency" or "Her Excellency," followed by the full name of the ambassador. The second line should say "The Ambassador of," followed by the name of the country that the ambassador represents; this is followed by the mailing address, beginning with the name of the embassy, if appropriate.
When sending a letter to a retired U.S. ambassador, especially a career diplomat, open the letter with the salutation "Dear Ambassador," with the ambassador's last name. For example, a letter addressed to retired Ambassador Bill Burns could open, "Dear Ambassador Burns." It is still appropriate to begin the first line of the mailing address with "The Honorable" before the retired ambassador's full name.