Some questions about e-mail in mac and Iphone

macOS & Mac Apps

Goodmorning all,
I wiould ask you 3 questions about E-mail in Mac and Iphone:
1. How can i, in Mac and in Iphone send a messagge to more than un adress, ad destinatary or as CC?, Itried to rwite the second one after ; but I think that it doesn't work. how can I do it?.
2. There is a way to set my mail in order to be notified when the destinatary read it?, how can I do, in Mac and in Iphone?, in Iphone, I know taht there is a thing called Notify, but when I try to press it, the message is blocked and I lost it.
3. I would like to creat a folder to archive there some messages taht are improtant but and so I want to keep, but that i prefer not to have them on the main folder, there is a way to do it?, in Mac or perhpas eisier, in the Iphone?.
Many thanks in advace, and have a nice day: