Dear Sir or Madam; Gentlemen
Formal, respectful opening phrase used in Japanese letters. Typically paired with a closing such as 敬白, 謹言, or 敬具. Used in business or official correspondence, not in casual writing.
Dear Sirs, we are delighted to hear of your company's continued prosperity.
謹啓、時下ますますご清祥のこととお慶び申し上げます。
Dear Sir or Madam, I hope this letter finds you in good health.
Compound of 謹 (respectfully) and 啓 (to open, to state). The exact historical derivation is uncertain, but the phrase has been used in formal Japanese correspondence for centuries.