WP SendGrid routes all emails through SendGrid to improve deliverability
By sending all emails through SendGrid, you can help them end up in an inbox, not a spam folder. SendGrid provides a high-deliverability email service, protecting your emails from overzealous spam filters. WP SendGrid uses SendGrid's API to make sure your site's emails are delivered. This helps ensure reliability for plugins that notify subscribers of new posts, verify new user emails, and perform other email-based tasks.
If you do WordPress development on Windows, or are hosting your site on Windows Azure, this plugin is an easy way to make sure your emails can be delivered. Because Windows doesn't have a built-in sendmail service, WordPress can't send emails by default, but since WP SendGrid routes all emails through the SendGrid API, they will be delivered, even if you're running on Windows.
To install, enable WP SendGrid like you would any other WordPress plugin. Enter your SendGrid credentials (you'll need a SendGrid account), and you should be ready to go. If you wish, you can also choose between SendGrid's REST API and their SMTP servers, and whether to connect to SendGrid using a secure connection.