alt Hacker NewsI don't know the US law, but surely in Europe specifically every private conversation is private, period. No matter if it's work email, your company cannot read the emails directed at your company mailbox by its initiative (of course in case it's needed a judge can ask it to be taken as evidence), nor it can read the files on your computer, or anything similar, no matter if the device it's company provided, because it would be considered the same as using a camera to spy on the employee, that is of course illegal.
Of course if it's shared communication media (e.g. a mailing list) it can, but not at your private address, no matte if it's @company.com, it's considered the same as your private email.
It heavily depends on country if employer can access the email or not. For example in Italy:
> Italian Supreme Court case law according to which defensive controls may be carried out where there is a well-founded suspicion of unlawful conduct, provided that an appropriate balance is struck between the employer’s interests and the employee’s dignity and privacy, and that the control concerns data acquired after the suspicion arose.