Step 1: Convert the reporting verb. The indirect reporting verb 'asked me' is converted back to the direct 'said to me'.
Step 2: Remove the conjunction. The conjunction 'if', used for yes/no questions in indirect speech, is removed.
Step 3: Revert the tense and pronoun. The indirect pronoun 'I' refers to the object 'me', so it reverts to 'you'. The Past Perfect tense ('had posted') reverts to the Present Perfect tense ('have... posted') to form the original question.
Step 4: Add punctuation. Quotation marks and a question mark are added to frame the direct speech, resulting in: He said to me, “Have you posted the letter ?”