Possible Clues:

• Where he, Ma and I have been posted
• Signed and sealed, but not delivered
• Like the check, often
• On its way by post
• A posting for a knight in armour?
• A posting for the knight
• I catch them entering, on their way to you
• Has the knight 16 down been posted?
• Armoured as well as posted?
• How an armoured knight might have been posted