Postman Pat Always Rings Twice

From Wiki and Wiki:

Postman Pat Always Rings Twice is a 1946 British computer-animated comedy film-noir based on the long-running BBC children's series of the same name by James M. Cain. This adaptation of the novel features featuring Postman Pat (voiced by Stephen Mangan and Ronan Keating), Lana Turner and John Garfield.

Pat Clifton, known as “Postman Pat”, is a friendly postman turned drifter who stops at a rural diner for a meal, and ends up working there. He wants to take a beautiful young woman, Cora Smith (Lana Turner), and her much older husband, Nick (Cecil Kellaway) on a late honeymoon to Italy.

He plans to afford it by a bonus he’s going to get from his employer, the Special Delivery Service (SDS). But Frank and Cora start to have an affair soon after they meet.

When Pat arrives at SDS Headquarters after finishing his round, Frank and Cora scheme to murder new boss Edwin Carbunkle (voiced by Peter Woodward), who has cancelled all bonuses and plans to make SDS more efficient, thinking that being friendly is a waste of time.

Their first attempt at the murder is a failure, but they eventually succeed and win the holiday to Italy, so Wilf is happy too, and all is forgiven.