Employees need to know that any piece of mail (business or personal) that is delivered to the company will be processed according to company procedures which may mean that it is opened and read by someone other than the intended recipient. 

You should have a policy prohibiting employees from using the workplace for their personal mail and clearly stating they have no right to privacy and that their mail will be opened. There should also be a disclaimer in case mail is lost in the office.

If an employee needs to have something delivered that is time-sensitive or needs to be signed for (such as loan paperwork), then require that they notify the mailroom and management first to make sure they are directed correctly.

Finally, ask employees to respect the privacy of others if they inadvertently see personal correspondence. 

Affinity HR Group is BSCAI's endorsed HR partner, providing HR support, recruiting and employee engagement services.  For a link to our menu of services for BSCAI members, go to www.AffinityHRGroup.com/BSCAI