Re: What if...
Even if they inform the employees, it is illegal to log their personal communications - they can only log official business communications...
There is a slight workaround, because most email servers, like Exchange, can't differentiate between private, non line of business and line of business communications and therefore logs everything in unalterable form (legal requirement in Germany, all business related (sales, purchasing, customer / supplier contact, internal discussions over projects and customers etc.) have to be stored in unalterable for for 10 years). So it is okay to store those private messages (without reading them), if they have informed the employee that the email system is only for business use, that for regulatory reasons the email will be stored and therefore employees shouldn't use email for private messages.
Again, even here, they cannot go snooping the emails, they can just store them, so that they are available if there is an audit and the emails are required (even emails the user deleted are stored in a regulatory/legal archive in Exchange, if the feature is turned on - not sure of the English name for the feature).
Keylogging and monitoring web usage is however illegal, even if the employee is informed, as is reading employees email. As said, by the court, there are exceptions, if the company believes that an employee is doing something illegal, for example.