Email going to a user at a similar domain name

Ignore them. It's not your job to manage mail on behalf of other companies. If the mail was sent to your system, whether by mistake or not, the mail is yours, not theirs. Sooner or later someone might notice that they're not receiving their messages and then they might look into it, hopefully ending with them telling the sender to use the correct address. In the meantime that's not your problem, so don't make it yours.

You could also consider disabling the catch-all address and simply reject mail to unknown users, so the sender gets immediately notified via NDR that he mistyped something.

As a side effect this can reduce the load on the mailserver massively since you don't have to process spams to randomly generated adresses in your domain.