Shut off email fetching.
log into the account (using a webclient or standalone client) delete the emails.
edit the ticket to make sure that the email address is correct.
Whats the bounce message say? Does it say that it will keep trying to deliver the email or is it a fatal error? If its fatal you can turn mail fetching back on. If it is going to keep trying hopefully it will tell you how much longer it will "attempt" to deliver it. Which means chances are it will generate additional bounce messages.