She is very serious about her Clients Confidentiality and will avoid talking about what she reads on people's letters. However, before she became a mailer, she was a thief and loved gossiping. When she met Newton Belduke, he suggested she become a courier since her only skill was being fast on her feet, and taught her the importance of not giving people's private information away.
Lettie is shown to have a crush on Jean Greyerl before she discovers that she's actually a girl. However, in the credits, there is a scene where Lettie is hiding in the bushes, looking at Jean and holding a love letter and flowers, suggesting that Lettie still likes Jean.
- Her name, Lettie Mailer, is a pun on her occupation as a letter courier, with "Lettie" deriving from letter, "Mailer" deriving from the term of the same name which describes someone who delivers mail.