"Re:" in a formal business letter

English as a Second Language English Vocabulary, Grammar and Idioms
1

Hello.
Where does “Re:” go in a formal business letter? Shall it be before or after the greeting?:
A)

  1. Address
  2. Re: Contract No…
  3. Dear Sirs:
    We are pleased to inform you that…
    B)
  4. Address
  5. Dear Sirs:
  6. Re: Contract No…
    We are pleased to inform you that…

Which word order is correct A) or B)
Thanks in advance.

2

either. I’ve seen it both ways.