Groups.io vs listmonk

Groups.io has no write-up on Specifiction yet; its figures are above.

listmonk is a free, open-source, self-hosted manager for newsletters and one-way mailing lists. It supports single- and double-opt-in subscriber lists, SQL-expression segmentation and management of millions of subscribers. Built-in analytics cover campaign performance, bounces and top links. Email templates can use Go expressions and functions, and can be built with a drag-and-drop editor, WYSIWYG editor, Markdown, HTML or plain text. For campaign delivery, listmonk runs multithreaded email queues across multiple SMTP connections and supports throughput and sliding-window rate limits. Its API sends transactional messages from predefined templates, including through messenger interfaces for email, SMS and WhatsApp. Campaign messages can also go as JSON to messenger web services for delivery through services such as SMS or FCM. Dashboard features are available through REST-like HTTP APIs using JSON, with BasicAuth or authorization tokens. Authentication includes OIDC single sign-on, and user and list roles support granular permissions. The software offers binaries for Linux, macOS, Windows and other operating systems, plus a Docker image. Running listmonk requires PostgreSQL version 12 or later.