mailerlite.com has a free tier for 12,000 emails per month but limited to 1,000 subscribers. If you don't mind writing a bit of javascript, you could use Cloud

mailerlite.com has a free tier for 12,000 emails per month but limited to 1,000 subscribers. If you don't mind writing a bit of javascript, you could use Cloudflare workers which allow sending emails via MailChannels API. Be sure to setup certificates so people cant spoof your domain.