Most government officials have email and some even "Twitter." These may work for informal communication, but the most effective way to connect with an official is to clearly and concisely commit ideas to paper in a registered letter or converse in person. Addressing your letter correctly or using the proper salutation in conversation insures that what you say will command attention--and a reply.
The Office, Not the Occupant
Much has changed since Emily Post published her first collection of rules of etiquette in 1922, but the concept of etiquette as a common language of social behavior has persisted. We address our elected and appointed government officials in specific ways, not so much as an expression of respect for them (although many deserve such respect) as for the office that they occupy. The titles and salutations that we use are based mostly on custom. Some, like the Massachusetts governor's salutation of "Your Excellency" are dictated by state law and date back centuries. Some, like "Mr. President," are based on an official's (in this case, George Washington himself) insistence on breaking with a tradition. Each office carries with it a set of responsibilities and privileges but, at least in democratic nations, the office represents the people who fill it and salutations are designed to reflect that concept, not to convey an image of personal power.
The first rule of salutation is to use the proper title. For example, all judges are not alike; some are magistrates, some municipal or circuit judges and some are Supreme Court justices. The proper salutation should include the tile of the office and the person's surname, as in Justice Sotomayor and Chief Justice Roberts.
Using given names would be considered too familiar, but complete names are used with "The Honorable" in an address, similar to the way "Mr." or "Ms." is used in business: The Honorable Judge of the 7th Judicial Circuit Court of Michigan, John A. Gadola The Honorable Chief Justice of the Wisconsin Supreme Court, Shirley S. Abrahamson
Using these address forms or other descriptive information would make a salutation awkward, so the second rule is to use the briefest form of the official's office with a last name or "Mr." or "Madam" (following Washington's example). The briefer forms allow the salutation to flow easily into the body of the letter or the conversation. Most officials, including members of Congress, state legislatures, governors and mayors can be greeted in the same way, by using their office (Representative, Senator or Governor) and last name in salutation: Mr. Mayor Mayor Wiggins Madam Attorney General Attorney General Blaine
Once upon a time, rulers were addressed with superlatives like Your Highness or Your Excellency. Over time, though, manners change. Most etiquette guides and many government departments publish proper forms of address, salutation and closing for many government officials, and some variations are inevitable due to internal protocols and the date of the guide's most recent revision. The U.S. Department of State's rules of protocol are usually the most reliably current; diplomats are in a critical position and can't afford to offend anyone. For most of us, though, if we remember the idea that we're addressing an office and that we should use the correct title in its briefest form, our salutation will be proper whether used in a business letter or reception line.