Mailjet for WordPress is a plugin that reconfigures the wp_mail() function to use Mailjet SMTP instead of mail() and creates an options page to manage the settings.
The plugin features reporting tools with advanced statistics to monitor and optimize your emails. There is also an API and dedicated module for WordPress.
Mailjet has paid and free options.
Plugin homepage: www.mailjet.com/plugin/wordpress.htm
Download: http://wordpress.org/extend/plugins/mailjet-for-wordpress/