Take a Letter is episode 17 of family guy season 14. It was originally aired on April 17, 2016.
To pay for Stewie’s private school, Lois becomes a postal worker. She finds a letter from Peter that was never sent to his old fling, Gretchen, dated a week before their marriage. When Gretchen tries to come between Lois and Peter, Lois has a plan of her own.