Lettie Mailer is Labyrinthia's only courier. She is hard-working and dedicated to her job, although she does have a habit of shouting "sir" so loudly that it leaves those around her with ringing ears. Mailer was a witness in Maya Fey's witch trial.
Her Japanese given name (Reda) is a play on the English word "letter", while her surname comes from the Japanese term for "postal service".
Both her English given name and surname are references to her job; "Lettie" is a play on "letter", while a "Mailer" is someone who sends mail.
Her full French name, "Colette Paustal", is a play on "collecte postale", meaning "postal collection".
Her German given name "Pia" may come from the Latin word for "devout/dutiful". This would make her full name mean "devout/dutiful post", which would be suitable considering how devotion she is to her occupation.
Her name in the Spanish and Italian versions is "Miss Iva", which is a play on the Italian word "missiva", which translates as "missive" (a formal term for a written message, letter, note, or memo) in English.
Her Dutch given name "Brigtje" is a play on "berichtje", which translates as "(short) message", while her surname "Poste" is a play on "post". Her full name could therefore be a play on "berichtje posten", which means "to post a small message".