I will be writing a letter and I want to address it to many people. Including the Pres. And members of Congress. I feel that Dear Sirs/Madam is not formal enough. Is there another way to address this letter? Also, Do i name everyone i plan to write it to? Do I write

To. Mr. AAAAA, Mrs. BBBBB, Pres. Obama, Dr. CCCC

or do i name one person at the top and

CC everyone at the bottom?