Newbie Question: Mailserver security
I have a problem with one of my client; he accuses his ISP of forwarding his email to the competition. So I was wondering what kind of action a hacker needs to take to realize this. I know that nothing is impossible but, is it plausible that this happened to my client?
The ISP assures us that this didnít happen and I tent to believe them. So to get it clear if that the client has another security leak I need to get a global view of all the possible actions of a hacker. So I can create an overview and search for other possible leakages.
Can somebody help me with this?