Hi, I've a huge problem with bounced mails. Now I'm in the blacklist for spam

Is this mod the solution to bouncing email? I've thousand of these:
Code:
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
ilgabbiano24.pt@gmail.it
SMTP error from remote mail server after RCPT TO:<ilgabbiano24.pt@gmail.it>:
host mx1.gmail.it [84.19.190.13]: 550 5.1.1 <ilgabbiano24.pt@gmail.it>:
Recipient address rejected: User unknown in virtual mailbox table