In a letter, where would you need to put a comma? after the salutation before the closing between each paragraph after your signature

I think that it is after the salutation or before the closing of the letter. If it were a letter, it would look like this:

Dear Dr. Doctor,
       (Dear is the Salutation). Body of letter. Body of letter. Body of letter. Body of letter. Body of letter. Body of letter. Body of letter. Body of letter. Body of letter. Body of letter.

                             Sincerely,