Reading employees email post 1: Is it OK to read employees’ e-mail as a security measure to ensure that sensitive company information isn’t being disclosed

Reading employees email post 1:
Is it OK to read employees’ e-mail as a security measure to ensure that sensitive company information isn’t being disclosed? 
In my view it is not a fault to read employ’s email as a measure of security. This ensures the Organization leadership and clients that the data is secured and no employ is involved in illegal data movement or data copy. This keeps the company safe from inside intruders.
2. Should you have access to those emails and files on a personal device that is accessing the company data via a 3rd party app (i.e. Outlook Mobile, or iOS default mail program)? 
Employees should be given access to company’s data using personal devices provided the company has secured data check and email verification if any data is misused. So it is not recommended to give access to certain applications through personal devices if the company’s secure wall is not proficient and if the applications have default password or shared password which will create a problem to audit to find culprit.