Many employers allow employees to use email, but have policies that state that the employer is free to monitor email. Many cases have held that, depending on the facts, the employee cannot assert privilege under those circumstances: both in claims between employee and the employer and between the employee and a third party.
This doctrine bit another employee recently, in a New York Appellate Division case, Peerenboom v. Marvel Entertainment, LLC, (N.Y. App. Div. March 16, 2017), available here. The court found spousal privilege and attorney client privilege waived because the employee (the chair of the company) lacked a reasonable expectation of privacy based upon application of the four factors from the leading case.
Any time a lawyer is aware that his client is sending emails from an employer, he should consider whether privilege will be deemed waived, and, conversely, lawyers should look to see if the opponents are doing this, and so waiving privilege.
This is not a new body of law, but it continues to bite people.