The best free email marketing software is Mautic. However, you will need to install it in your web server and integrate it with Amazon SES smtp which allows you to send upto 63,000 emails per month for free. The installation process requires basic in Knowledge in web development.
Here is a list of open source and free email marketing software that are self-hosted (require software installation in your web server): https://emailmarketingwp.com/free-email-marketing-software/
If you need a free version where you do not have to setup anything then Mailchimp has a free plan of upto 2,000 email subscribers. Just create your account and you are ready to get started. Another alternative to Mailchimp is ConvertKit which offers a free plan of upto 1,000 email subscribers.