By default, your mailbox opens with the Inbox view. All messages in your Inbox are displayed in the Content pane. You can change the initial view to be any of the folders, searches, or tags in the Overview pane. Make these changes from Preferences>Mail>Displaying Messages>Default Mail Search.
Examples for how to display only specific messages when you open your mailbox:
To display only your unread messages when you open your mailbox, type is :unread in the Default Mail Search field.
To display email messages that are tagged with specific tags, type tag:< tagname> in the Default Mail Search field. For example, to display only messages marked with the ToDo tag, type tag: ToDo.
To display messages that you sent to a specific folder via an email filter, type in:< foldername> in the Default Mail Search field. For example, to display messages in the Work folder, type in:work.
Note: Use quotes if the folder or tag is more than one word. For example in:"Unread Email."
In the Preferences>Mail> Displaying Messages section, enabling one of the options in When I click Get Mail sets whether or not your mailbox view changes when you click Get Mail.
If Run my default search is selected, when you click Get Mail, the mail search described in the Default Mail Search field is run. If your default search is not the folder you are viewing, your view is automatically redirected to the default folder view. In most cases, this is your Inbox.
If Update my current view is selected, when you click Get Mail from a folder, the Get Mail request searches for updates to your current folder view and for other new mail. Your current folder view does not change.
Note: If new mail is received to other folders, those folders are changed to bold and the number of unread messages is updated.