This plugin is intended to significantly improve user management, easily create contact forms, and keep track of incoming shortcode form messages.
WordPress already comes with some basic user management functions - WP-CRM expands on this functionality by allowing you to organize your users using custom attributes, find them using filters, and keep track of correspondence.
Your WP control panel can effectively be used to manage all your customers, vendors, partners, affiliates, etc.
WP-CRM on GitHub
If you found the default functionality of WP-CRM is not enough for your needs please take a look at the list of available Add ons
Ability to send newsletters to users, or user groups. More about Add-on