Personal emails at work are sometimes protected from intrusion and sometimes not.  The email system belongs to the employer.  One indicator that work generated emails may be protected occurs when the employer allows some personal use of email.  See the case discussed at one blog post.  But, see another case discussed at a different blog in which the employee’s emails were found not to be protected from review by the employer.  The biggest difference in the two cases is that in the first case, the employer did allow some personal use of the employer’s email system.  That court found that yes, the employee had a reasonable expectation of privacy in such a situation.