Virbl is a project of which the idea was born during the RIPE-48 meeting. The plan was to get reports of virusscanning mailservers, and put the IP-addresses that were reported to send viruses on a blacklist.
We don't block anything. We only provide a list with IP's which have sent viruses to us or one of our contributors.
The people using the list are the people that decide how they which to implement it. Some use it to give messages a score in spamchecking, others use it to completely block messages from a listed IP. BIT is not responsible for blocking your mail. If blocking happens, the recipient chose to do so.
We will list an IP after it has sent two virus-emails to one of our sources. (See the contributors page.) We will remember that you sent those emails for seven days. You will only be listed as long as the last time we 'saw' you sending viruses is less than 24 hours and the total sent emails is greater than two, in the last seven days. So if you've fixed the problem, you will be delisted automatically in 24 hours.
If those messages contain viruses, you're not innocent. You are sending viruses around, you're just not originating them. Scan messages before you forward them. There are free virusscanners available, have a look at Amavisd and ClamAV.