So many reasons:
- Security Risk
- Legal Liability
- No Plausible Deniability
- Not Scalable
- Memory and System Requirements
- Unnecessary and Redundant
- Unproductive use of his time
- There are better ways to monitor employees
- Et cetera.
The biggest reason is the security risk. If someone stole his computer, or hacked into it, they would not only get his email, they would get all the email of the entire company, including any trade secrets and confidential information they may contain. Sure, all that information is on the mail server, but the mail server usually has much better security attached to it.
The second is that it is redundant. If he needs access to an employee's email, he can get access to it through IT. He doesn't need it popping up on his computer in real time as well.
And if he is looking at everything, he is focusing on nothing. There is no way he can keep up with emails everyone in the organization sends and received. If he has specific concerns about particular employees, then look at those email accounts. It's more focused and a more productive use of his time.
If he is concerned about certain types of emails, a system can be put into place that flags emails and employees that might need to be reviewed.
Another issue is memory usage. Is his computer actually going to be able to handle 100,000 to 1 million emails in Outlook (or whatever mail client he is using). Probably not.
Besides all of this, such an invasion of people's privacy could cause a hostile working environment, and harm productivity.
Then you have the legal liability. If the CEO gets a copy of every email, and he does not read all of them, and one of the employees does something bad that the CEO does not catch, the CEO could be accused of approving the conduct or casting a blind eye. Instead of the CEO having plausible deniability, prosecutors might accuse him in being complicit in a crime, simply because he did not read every single email the organization sends or receives.
And, this is not scalable either. The more employees he has, the less he will be able to review all the emails. The bigger the organization, the more likely he will be held accountable for an email he didn't have time to read.
There are much better ways to monitor employees than this.
For example, if he really needs that much control over what employees say and don't say, then create a compliance department that spot checks employees, or implement a ticket system which tracks all emails in and out of the system that can be logged into and spot checked from time to time.
Many systems work with email that give advanced functionality, such as:
- ticket systems
- project management systems
- team collaboration systems
In fact, such a system, that he can log into anytime, might be a much better solution, and give him the access and sense of security he is looking for.
Setting up his computer to access everyone's email account is too risky.