What should I do to set up postfix for several domains that is not listed in the library page ?
The Postfix guides in the library enable the use of virtual domains. If that's not what you need, be more specific about what you want to achieve.
You can mention users to notify them: @username
You can use Markdown to format your question. For more examples see the Markdown Cheatsheet.
> I’m a blockquote.
I’m a blockquote.
[I'm a link] (https://www.google.com)
I'm a link
**I am bold** I am bold
*I am italicized* I am italicized