Email marketing lets you communicate directly with people who have already shown interest, without depending on a social platform's algorithm. Growing a list ethically means getting explicit opt-in consent -- through a website sign-up form, a lead magnet like a free guide, or a checkout process -- rather than adding people without permission, which damages trust and can get a sender's emails flagged as spam. Tools like Mailchimp or Brevo (formerly Sendinblue) offer free tiers suitable for small lists and let you segment subscribers by interest or purchase history to send more relevant messages. The two core metrics to track are open rate (the percentage who opened the email) and click-through rate, or CTR (the percentage who clicked a link inside it) -- both help you judge whether your subject lines and content are working.