In conversation, simply use "Senator Smith". The salutation for a Senator, former or current, is "The Honorable", so in introductions you would introduce her as "The Honorable Jane Smith, former United States Senator from California."
"The Honorable John Doe" (on an envelope) and "Dear Sir" (in a letter)
As a courtesy , he may always be addressed as Senator. Just be careful not to mislead anyone to thinking he is the current or sitting Senator.
Either "Congressman Jones," or "Mr. Jones" is correct. Congressmen and Senators carry their rank away from the job, as do other high government and military officials.
Sir.
Senator Grassley's email address
Yes, from Illinois.
Earth Day was founded by former Wisconsin senator, Gaylord Nelson.
US Senator from Illinois. Prior to that he was a state senator from Illinois.
Barack Obama
Former US President Ronald Reagan
Daniel Akaka's address is not listed to the public. He is a former United States senator and United States representative.
Address him or her as "Honorable" as in the Honorable John McCain. The "Honorable" is only for adding before the name in addressing an envelope and on the top of the letter where you put the full name and address of the senator. In the body of the letter you would write "Dear Senator McCain;"
Senator Daffy Duck US Office Building Washington, DC
I address letter to former state representative as US representative.
Bill Bradley
Before he became president, he was a US Senator from Illinois.