Salutation for a current Ambassador is His or Her Excellency. Also Ambassador and last name of and country. I believe that since former military and President and Senators etc.....retain their title....Like President Carter.....and military usually has Ret. after the last name I think as a salutation on an Envelope it would be His Excellany John A. Gavin, Ret.
Dear Mrs Ambassador..
Dear Mrs. Obama,
On the Envelope His/Her Excellency Mr./Ms./Dr./Rev. [name] Ambassador (or High Commissioner) of [country in full] In letter Dear Mr/Mrs Ambassador
No honorific is required when addressing the former chairman of a committee.
In a letter to a Caribbean ambassador, the appropriate salutation is "Your Excellency." This formal greeting acknowledges the ambassador's diplomatic rank and position. Following the salutation, it is customary to address the ambassador by their title and last name, for example, "Your Excellency, Ambassador Smith."
"Your Honor" or "Mr. (Mrs.) Mayor"
The proper salutation when addressing a letter to a former president of the United States is "Dear Mr. [Last Name]." For example, if you were writing to former President Barack Obama, you would begin with "Dear Mr. Obama." It is respectful and acknowledges their status while using a straightforward, formal address.
The salutation for a former judge is typically "Judge [Last Name]" if you are addressing them formally.
His Excellency, Ambassador of ................... This salutation can be used when writing to the Forein ambassadors of all countries.
An ex-ambassador is often referred to as a former ambassador or a retired ambassador.
The proper title for a retired ambassador is "Ambassador (Ret.)"
Many people will call him Senator as a mark of respect. In writing he could be referred to the Honorable xxxx or former Senator xxxx.