Email Appending
Email appending is when you use a third party to add email addresses to your existing customer records based on other details like name or postal address. It is risky because these people did not ask to hear from you, which often leads to spam complaints and poor deliverability.
Email appending happens when you have customer records without email addresses and you hire a data vendor to fill in the gaps. They match your data against their databases and give you what they believe is the right email for each person. On paper it looks like a fast way to grow your list. In practice you are adding emails for people who never asked to hear from you.
That lack of consent is the core problem. These contacts are more likely to ignore your messages, mark them as spam, or complain. Over time this hurts your sender reputation so even your real subscribers see more emails in spam. In some countries using appended emails for marketing can also create legal risk if you do not have clear permission.
For most teams the better move is to collect emails directly from customers. Ask for an email address at checkout, in support chats, or by sending a simple postcard that invites people to subscribe. Make the value clear, like order updates or a small discount, and let them choose what they want to receive. You end up with a smaller list that performs better and keeps you in good standing with inbox providers.