Related Clues:

• Double-helix molecule
• Drop in a letterbox
• Letters, collectively
• Biological ID
• Drop in a slot
• Twisted sample
• It's not delivered on Sundays
• Genetic code container
• Postal sackful
• Attire for Galahad
• ''CSI'' evidence
• It contains a lot of letters?
• Code to live by?
• Initially, it stores genetic information
• Post or body armour