Working office , I know a thing or 2 about IT , that's my Degree. Your email could be potentially have been used to receive emails where a separate dedicated business email address should have being setup instead. E.g
liveservices@companyit.com . The truth is that if your manager wants to see emails that are relevant to him , then he should see them as a cc , bcc to his own email address. If he wants to see other person emails , he should be going through admin , and he should have a good professionally sound reason for (btw you should generally be unaware of it). Regardless this is either poor work practice or indeed a decision made using poor professional standards on his part.