“Listwashing” is defined as the removal of spamtraps and the email addresses of “complainers” or “litigators” from a list that is not confirmed-opt-in, while retaining the other email addresses. This is often used as an attempt to clean up a rented, purchased, or very old mailing list.
“Waterfalling” is a technique wherein a list owner “waterfalls” the same illicitly obtained address list through a series of usually unknowing, innocent ESPs, each time cleaning bounces, complainants and maybe non-respondents, with the end goal being to send the final result through a good ESP with solid deliverability. The result of this process is damage to the reputation of each ESP involved, as well as being a violation of ethics, counter to best practices and against Spamhaus policy.
Some verification/validation companies offer a service that promises to remove “spamtraps, complainers, litigators and all other perceivable threats” from email marketing lists. However, the presence of traps highlights a data collection problem. Going trap hunting is merely treating the symptom.
The focus should be on fixing the collection issues, and segmentation of the existing list with exacting care, with close attention paid to recipients that do not engage. These services go against the best practices of building a legitimate and successful email marketing list. Also, these services simply do not work as claimed: Spamhaus frequently sees mail in its spamtraps from “cleaned” lists!