Spamhaus has begun blacklisting major retailers for typos in email addresses. The incorrect addresses are thought to be the result of the retailers' e-receipt programs that allow a customer to enter an email address at the point of sale in order to have a receipt emailed after the purchase instead of printed out. Spamhaus blacklisting can suppress email delivery by as much as 60%.
Spamhaus is being completely reasonable in this approach. Consumers can write down any address whatsoever when they check out, causing unwanted marketing communication to blast out to an unsuspecting recipient. Ever heard of double opt in?