Is it possible to use Cloudflare's free plan with an SMTP provider for sending emails?

Yes, Cloudflare's free plan works perfectly fine with any third-party SMTP provider. Cloudflare's free plan primarily provides DNS management, CDN, and basic security features. As long as you can configure the necessary DNS records (MX, SPF, DKIM, DMARC) within Cloudflare, you can use any SMTP provider to send emails from your domain, regardless of your Cloudflare plan.