Actually it doesn't really mean his email address has been hacked. All it means is his address has been harvested and used as a reply to address on bad email. I have had those sort of emails to myself looking like they are from myself ... but they aren't. No hacking is required to make an email look like it has come from an address that it didn't really. There is not a darned thing we can do to stop it either. People just have to be wary when they get emails that seem to come from people they know that don't look like the sort of email they would expect from them. If it is a link or file attachment and looks suspicious always email them back and check they really sent it. It is always very easy to recognize these fake emails.

Because my email address is on the bottom of all pages here at Synth Zone it has been getting harvested for years now.

You can see for yourself how easy it is. In whatever email program you use to send email just change the "Reply To" address to be anything you want and any email will appear to come from that address.