Well, the problem here is obviously not the nick but the inability of someone to drop an old email address or just forward it to another one. You don't have to have it in your mail client. You can manage that from the webinterface and never again login to that mail address.

I'm/was doing quite a lot IT support for friends, family their friends and so on and have never heard of anything like that. I'm also sure that the domain @hotmail.com would be enough to not get you a job on certain businesses.

> One of the more common office security failures is to have your email client auto-fill to someones personal account instead of their company-issued account

So...you are sending private emails from your business account? Again it's not the nick/names problem. The problem is your behavior. This is the root cause here and doing some make up won't solve your problem.