This isn't strictly a Fusion issue, just a practical consideration of switching.
I try to convince all my friends to separate their "permanent" email addresses from their ISPs, just so they don't run into this type of problem.
I'm tired of receiving "my address has changed..." emails (usually sent to 75 people, with all addresses on the "To:" line). [Why isn't use of BCC part of Email 101?]
Just stick with Sonic.net forever and this isn't a problem.
This is just about the only legitimate use of BCC that I see in my personal mail. I've been sorely tempted in the past to simply filter out anything that wasn't explicitly directed to me by "to" or "cc."