Manage millions of subscribers across multiple mailing lists while sending campaigns through multi-threaded SMTP queues that handle high throughput efficiently. Segment audiences using SQL expressions, send transactional messages via simple API, create dynamic templates with Go templating including over 100 functions, write content in WYSIWYG editor or Markdown, upload media to filesystem or S3 storage, connect webhooks for SMS and WhatsApp delivery, and provide subscribers complete data control including export and deletion options.