Possible Clues:

• b, d, f, h, k, or l
• Character's upright like carbon stopper
• A person posting a letter, we hear -- someone coming up the hill?
• Part of letter read out by a man in Post Office?
• A correspondent welcoming the beginning of chatty part of letter
• Part of letter one posts, say
• One rising in rank, e.g
• Feature of a lowercase b, d, f, h, k, l or t
• Climber found in only one part of garden
• Feature of lowercase h's and k's