They can't monitor that but should forbid anyone from using it for company work and may forbid you from using it while on their time. It all comes down to risk. If I'm in charge of a company network there is no way for me to know if someone's home PC has a virus/worm/whatever that could affect my network. Then there is the legal liability should someone you have offended trace your e-mail back though the company network. Even if as you said you have personal equipment at work with your own connection there is the abuse of company time when your checking your personal accounts on the company $. Then there are issues where someone else doesn't like the company and sends spam out faking your e-mail address and the company has to prove that it didn't come from them and in the process finds mail from you on your own equipment and now you have to prove you didn't send the spam. Then there is the potential for the disgruntled employee to steal company secrets when he finds out he is getting laid off.