1. Opt-in Forms: Use forms on your website, social media, and other platforms where users can voluntarily provide their email addresses. 2. Lead Magnets: Offer valuable content like eBooks, webinars, or discounts in exchange for email addresses. 3. Events and Webinars: Collect email addresses during events, webinars, or trade shows. 4. Purchased Lists: Although not recommended, some businesses purchase email lists. Always ensure compliance with GDPR and other regulations.