In The Sims, and on college lots in The Sims 2: University, they deliver bills every three days. In The Sims 3, and on non-college lots in The Sims 2, they deliver bills on Tuesday and Thursday. They also come by to collect paid bills from the mailbox. In The Sims 2 and The Sims 3, they may also deliver items such as love/hate letters, books and mounted fish.
In The Sims, the mail carrier is known as "Carrie the Mail Carrier". She has dark skin, a wide body, and wears a blue mail carrier uniform. She cannot be interacted with in any way. Like all NPCs in The Sims, she arrives and leaves on foot, and will teleport away if her route is blocked.
In The Sims 2 and The Sims 3, mail carriers become full-fledged Sims, and each neighborhood will have two or three. Sims can talk to them, ask them to hang out, and give them tips. In The Sims 2: Pets, dogs will go to the mailbox to greet them. Some dogs in The Sims 3 Pets will autonomously growl and chase the mail carriers away from the lot after the mail carriers put the mail into the mailbox. The dog's autonomous action will place as the next action after the current one even when there are more actions in the queue. Mails will be flown from the mail carrier's mailbag when they get chased by dogs which will disappear shortly after landing on the ground. The dogs can gain the aggressive trait if they regularly being aggressive towards the mail carriers if they didn't get scolded by their owners or their actions didn't get canceled by the player. Surrounding the mailbox with a gate locking from pets could be a way to prevent dogs to autonomously interact with the mail carriers. The uniform they wear is based on that of USPS.
In The Sims 4, mail carriers wear a uniform and deliver bills every Monday or Tuesday morning.
In The Sims 3: Pets, the mail carrier may sometimes walk up to a window of the house and look inside. If a Sim sees this, an action will appear titled "Stop Peeping Sim". This action may be cancelled from the queue.[confirmation needed]