MailPoet is a WordPress plugin that allows you to create and send newsletters, post notifications and autoresponders to your website subscribers. It has a number of features that allow you to easily design and customise the look and feel of your emails, manage your subscribers and track the performance of your campaigns. Some of the main features of MailPoet are:

Drag-and-drop email designer: Allows you to easily create professional-looking emails by dragging and dropping various elements (such as text, images and buttons) into place.

Customisable templates: Provides a range of templates that you can use as a starting point for your emails, or you can create your own custom templates from scratch.

Subscriber management: Allows you to import and export subscribers, divide your list into different groups and send targeted campaigns to specific groups of subscribers.

Autoresponder: This allows you to set up automatic emails triggered by certain events, such as when a subscriber joins your list or when a certain date or time is reached.

Email delivery: Uses its own servers to deliver your emails and ensure that they arrive in your subscribers' inboxes and do not end up in spam filters.

Overall, MailPoet is a powerful and easy-to-use tool for managing and sending newsletters, post notifications and autoresponders from your WordPress website.