SPAM doesnt do an ISP good (Score 1)

when spam causes a mailserver to be too busy to accept real mail (this really happens) who is responsible for the messages that arent received by the time the information has become stale?

I have had an instance where I received 100,000 peices of bounce mail from some a bulk email company and it stopped an important message to be delayed by 4 hours .... the message was telling the person that there was an important meeting they had to be at 1 hour before he got the message.