Short term, unfortunately basically nothing we can do - it's just a limitation of how email forwarding works. Bounces are caused by users with invalid/old emails, so the only way we could find them would be to pre-test each email for a bounce to determine if it was live. But that would make Tabroom look even more like a spammer than it already does, and keeping us off various blacklists is already a serious problem.
Tabroom does get the bounces, but forwards them on to the user who sent the email, otherwise all emails would have to appear as Tabroom, not as you. That is, it's easy for us to suppress replies being sent to you, but you also wouldn't get legitimate replies either.
Next time I see Palmer, I'll talk with him about whether there's some advanced email-fu that we might be able to figure out.