wp-includes/pluggable.php and post smtp

I installed Post SMTP https://www.ads-software.com/plugins/post-smtp/

and it shown

Postman: wp_mail has been declared by another plugin or theme, so you won’t be able to use Postman until the conflict is resolved.
More info that may help – /home/robin/sites/site-name/public/wp-includes/pluggable.php:173

I gone through the search and found that Content aware sidebar is calling this file from

/lib/freemius/includes/class-freemius.php

line 8212-8222

        /**
         * Load WordPress core pluggable.php module.
         *
         * @author Vova Feldman (@svovaf)
         * @since  1.1.2
         */
        private static function require_pluggable_essentials() {
            if ( ! function_exists( 'wp_get_current_user' ) ) {
                require_once ABSPATH . 'wp-includes/pluggable.php';
            }
        }

Could you please guide me what should i do now?