The practice of gathering email addresses from guests of a website is referred to as list building. This is done to expand the subscriber database and enable future commercial contacts with potential or current clients. However, the bad news is that with time, your email marketing contact pool will deteriorate.

Your contacts' email addresses may change if they move from one employer to another, opt-out of your email communications, or discard an address that was solely used to fill out forms on websites.
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