1. Through the Mailboxes listing, by checking the Users' names that should have access to the mailbox being added/edited.
Any User Name that has a checkmark in the User column will have access to that mailbox for viewing and responding on behalf of that mailbox. Anyone with the Owner column checked will have full access to the mailbox including the abilities to create folders and delete emails. In both cases, the User will be able to see the full mailbox contents (all e-mails), including seeing those in Advanced Search results and the Activity lists of Contacts/Companies.
2. In the Security sections Settings, by selecting the Filter level for the "Mailbox" entry.
The Default Filters in Settings control access to mailbox contents for all Users in the system. To set individual Filters per Role or User, edit the desired Role or User and selecting the desired Filter in the same way. The available filtering options are:
a. Use Default
b. None -- set this option to turn filtering off. All mailboxes' contents will be available to all Users.
c. Limit To User and Employees -- this sets the filtering so that the User can see their own mailbox and see any contents of mailboxes of Users that Report To them (as set in the Reports To tab of the User).
d. Limit to User -- this sets the filtering so that each User only sees their own mailboxes' contents.
e. Deny