Your comments

Yes, the addition of this card met the requirements i mentioned. 

Hello, Yes it concerns that type of cards 

Hi Eric,

Yes I'm referring to admin messages displayed on the home page, it looks like this :

In my case, the goal would be to differentiate admin messages depending on the type of user and not to multiply messages for one user..

So in fact, it means that a user should probably have multiple message windows. I think that, if we manage this in terms of groups, a user wouldn't have more than 2 message windows on his home page.

Moreover, that type of admin message isn't very long, usually it's like 2 lines of text maximum. So, I think it wouldn't use up lot of space on their screen.