The standard user permissions in Slate can grant access to given functions, but realms enable more targeted functional access restrictions to only objects contained within a realm.
Adding a realm to a mailing
Go to Deliver.
Select New Mailing.
Select a Realm.

Select Save.
Only users with access to the selected realm can view or edit the mailing.
😵💫 Don’t see realms as an option?
If your database doesn’t have any configured realms, they’ll be completely hidden from the user interface. Create your first realm to see them in User Permissions and database objects.