If a Manager is away for any length of time they can divert their notification emails to another employee to deal with any approvals etc in their absence.  It is simplest to divert these emails to an employee with Client Admin access in order for them to be able to act on the notification emails.

The email divert is found in People > Employee name > Person (dropdown) > Work - Untick Get Notification Emails AND select the employee to receive them instead.  If no one is selected the default choice is always used which is found in Admin > Settings > Email (dropdown) > Email - Alt [Alternative] Manager.