A purchased list is any list populated with the contact information of persons that you had to pay for to obtain.
The contacts in purchased lists have not elected to be contacted by the people who use purchased lists. When you do send them an email, they will not recognize your name or email address and, likely, mark your message as spam.
Unfortunately, this cannot be true. The list is filled with contacts who are strangers to the purchaser. Therefore, it is not possible that these contacts have opted in with you to receive emails about your business.
Companies that sell these lists may claim they are “Opt-in”, “Verified” or “Clean”. It is possible that the contacts in the list opted in to receiving emails from the seller of the list. But even in that case, they have not actually requested to receive emails from the purchaser of the list.
There is no guaranteeing the quality of purchased lists. They can contain dead, non-existent, or inactive email addresses. In some purchased email lists, there are planted email addresses. When you use one of these email addresses, you are flagged as a spammer.
It takes a lot of time and patience to build a large, quality list with contacts relevant to what you are marketing. The chances of finding such quality lists being sold that also fit your needs are very slim. The way many of these lists are created is by compiling old lists and taking information from public sources. By using one of these lists, you are damaging your reputation; you will likely get marked as a “dirty” sender. And in turn, this will negatively affect the delivery rate of your emails.