Strangerville Fan Mail

It's caused by the trait called Hero of StrangerVille, which comes when you complete the StrangerVille Mystery aspiration. As it is a reward trait, re-traiting potion won't help. So you must use cheats.

First you need to enable testingcheats:

testingcheats on

And then you have to enter this cheat:

traits.remove_trait trait_HeroOfStrangerville

When the trait is gone, your sim should no longer receive fan mail.

If on doesn't trigger the cheat to be enabled, use the word true.

You have to remove the Hero of Strangerville trait from your sim.

When your Sim defeats the Mother Plant they earn the ‘hero’ trait. You’ll have to remove the trait.

In the rewards list there’s a re-traiting potion. There might be cheats you can use to remove it if you don’t have sufficient points for the potion.