mailer opensource - SERP Analysis

https://listmonk.app/

https://www.thunderbird.net/en-US/

https://github.com/PHPMailer/PHPMailer

https://nodemailer.com/

https://mautic.org/

https://thecmo.com/tools/best-open-source-email-marketing-software/

https://www.reddit.com/r/opensource/comments/1ivvrx1/best_open_source_email_client/

https://www.useplunk.com/

https://opensource.com/alternatives/gmail

https://opensourcealternative.to/alternativesto/mailchimp