WP Mail SMTP: Don’t Save Outlook Emails to Sent Items

 /**

 * WP Mail SMTP: stop the Outlook mailer from saving a copy of every

 * sent email to the Sent Items folder of the connected Microsoft 365 account.

 *

 * Note: emails larger than 4 MB with attachments are sent a different way

 * by Microsoft and will still be saved to Sent Items.

 */

add_filter(

        'wp_mail_smtp_providers_mailer_get_body',

        function ( $body, $mailer ) {

                if ( $mailer === 'outlook' && is_array( $body ) ) {

                        $body['saveToSentItems'] = false;

                }

                return $body;

        },

        10,

        2

);