Many employees use their work email account for all types of communications. If you want any communication to remain private, do not use your work email for the communication. This is extremely important when you are communicating with your attorney. Communications between an attorney and the attorney's client are normally considered privileged communications and are therefore not discoverable in a civil or criminal matter. However, a client can lose this privilege if the client communicates with his or her attorney via the client's employer's work email. Then the communication becomes discoverable and its contents can be used against the client. For example, if the client is involved in a criminal matter and writes the attorney, "I did it, get me off", this could be used in court as an admission of guilt in the event the communication is not attorney/client privileged.
There have been many court decisions around the country regarding this issue. Most hinge on whether the employee had a reasonable expectation of privacy when using the company email system for private communications. However the expectation of privacy goes out the window when a company includes language in the company handbook which makes it clear that any use of the company systems is not private. Most company handbooks now have language which states that employees should have no expectation of privacy when using company systems. Such policies normally go on to state that all information on the company systems may be monitored, accessed, deleted or disclosed at any time without the employee's permission. To enforce this waiver of privacy, the company usually has the employee sign an acknowledgment which states that the employee has read and understands the company's policies. Such an acknowledgment is an admission by the employee that the employee knew about the policy and the fact that the employee has no privacy when using the company's systems.
There have even been cases in which the employee lost their expectation of privacy when the employee accessed the employee's personal email account using an Internet browser on the company's computer. Again, it depends upon the language in the company's policy. If the employee consents to the employer's monitoring of the employee's Web activity on your computer, then you won't have any expectation of privacy and those communications with your attorney may not be privileged.
Although your employer may be able to monitor your personal email from your work computer, your employer can't go beyond the workplace. The Stored Communications Act of 1986 prohibits your employer, or anyone, from approaching your personal email network provider to obtain your emails.
The lesson here is to never use your work computer for personal communications to protect the privacy of those communications.