Mailchimp's brand recognition means most people getting started with email marketing try it first, and for very small lists with modest sending needs, the free tier works fine. The 500-contact, 1,000-email/month free plan plus basic single-step automation gives enough room to learn email marketing without paying anything.
The honest 2026 assessment is that Mailchimp has been surpassed on value by competitors at almost every price point. Brevo offers more contacts and more daily sends for free. Omnisend includes more automation features. Klaviyo has deeper ecommerce analytics. What Mailchimp retains is familiarity and integration breadth. If you're already on Mailchimp and it's working, the switching cost may not be worth it. If you're starting fresh, the free tiers of Brevo or Omnisend are better deals.