Hi! I want to make sure that users know about a certain rule before posting in a certain category. Can I show a message to users before or after posting in this category and/or send an automated message via Dicobot or Email?

So you want those creating topics in that category to have some guidance? Have you seen What are Topic Templates?

Sending a message upon post

isaac (Isaac Janzen) September 19, 2022, 4:39pm 2

You could display a banner for a given category

Topic		Replies	Views
Show customisable message on private topics/categories? Support	5	1150	September 16, 2021
View only category Feature	17	2685	April 11, 2017
Welcome / About Message on a Category Page Support	9	1723	June 8, 2024
Display banner topic only to logged in users? Support	3	1305	April 17, 2019
Showing two banners: one to anonymous users, and one for logged-in members Support	5	1329	May 4, 2019