Sorry to have created this debate. Firstly, a disclaimer: please treat the question as a hypothetical scenario and eliminate all personal judgements. I think I now also recognised that law and culture (country and organisation) playing important roles also have quite diverse differences.

I find that a key problem is that it is difficult to hide confidential information from IT. I am not sure how we can effectively prevent this, but some organisations may accept this fact and hold the policy that you may view with good reasons, but cannot share data without permission.

It's certainly nigh-impossible to hide information from the IT staff managing the systems where it's stored on, but that is hardly the issue. Part of being a sysadmin is handling confidential information ethically and doing what the OP did is a clear violation of how sysadmins are expected to act. Just because they have the ability to read anyone's email if they so choose doesn't mean that they are doing so routinely.

It's not as if every email sent through the serves is visible in some sort of monitoring tool (unless specifically set up, but that's fairly Kafkaesque). It normally requires a certain amount of effort for admins to view information like this. If you do happen to catch something, for instance when fixing a setting on a user's email client, the normal response is for all that info to be treated as confidential, even from the employee's manager.

Roger's answer actually put this quite well: You may have access to sensitive information, but make no mistake, this does not automatically mean that you can look through it and act upon anything that you find.