source: https-redirection/trunk/classes/ehssl-email-handler.php

<?php

class EHSSL_Email_handler {

        public static function send_expiry_notification_email( $cert_data ) {
                $settings = get_option( 'httpsrdrctn_options', array() );

                $content_type = isset( $settings['ehssl_expiry_notification_email_content_type'] ) ? sanitize_text_field( $settings['ehssl_expiry_notification_email_content_type'] ) : '';
                $from         = isset( $settings['ehssl_expiry_notification_email_from'] ) ? sanitize_text_field( $settings['ehssl_expiry_notification_email_from'] ) : '';
                $to           = isset( $settings['ehssl_expiry_notification_email_to'] ) ? sanitize_email( $settings['ehssl_expiry_notification_email_to'] ) : '';

                if ( empty( $to ) ) {
                        EHSSL_Logger::log( 'Recipient email address could not be found to send expiry notification email.', 4 );

                        return false;
                }

                $subj = isset( $settings['ehssl_expiry_notification_email_subject'] ) ? sanitize_text_field( $settings['ehssl_expiry_notification_email_subject'] ) : '';

                $body = isset( $settings['ehssl_expiry_notification_email_body'] ) ? sanitize_textarea_field( $settings['ehssl_expiry_notification_email_body'] ) : '';
                $body = self::apply_dynamic_tags( $body, $cert_data );

                $headers = array();
                if ( ! empty( $content_type ) && $content_type === 'html' ) {
                        $headers[] = 'Content-Type: text/html; charset=UTF-8';
                        $body      = nl2br( $body );
                }
                $headers[] = 'From: ' . $from;

                try {
                        wp_mail( $to, $subj, $body, $headers );
                        EHSSL_Logger::log( 'SSL certificate expiry notification email sent to : ' . $to . ', From email address used: ' . $from );

                        return true;
                } catch ( \Exception $e ) {
                        EHSSL_Logger::log( 'SSL certificate expiry notification email couldn\'t be sent to : ' . $to . ', From email address used: ' . $from, 4 );
                }

                return false;
        }

        public static function apply_dynamic_tags( $body, $data ) {
                $tags = array(
                        '{label}',
                        '{issuer}',
                        '{issue_date}',
                        '{issue_time}',
                        '{issue_datetime}',
                        '{expiry_date}',
                        '{expiry_time}',
                        '{expiry_datetime}',
                        '{status}',
                );

                $values = array(
                        $data['label'],
                        $data['issuer'],
                        EHSSL_Utils::parse_date( $data['issued_on'] ),
                        EHSSL_Utils::parse_time( $data['issued_on'] ),
                        EHSSL_Utils::parse_timestamp( $data['issued_on'] ),
                        EHSSL_Utils::parse_date( $data['expires_on'] ),
                        EHSSL_Utils::parse_time( $data['expires_on'] ),
                        EHSSL_Utils::parse_timestamp( $data['expires_on'] ),
                        ucfirst( EHSSL_SSL_Utils::get_certificate_status( $data['expires_on'] ) ),
                );

                return stripslashes( str_replace( $tags, $values, $body ) );
        }

        public static function get_merge_tags_hints() {
                ob_start()
                ?>
        <div class="ehssl-settings-field-cat-3">
            <a href="#" class="ehssl-toggle toggled-off"> <?php _e( 'Click here to toggle email merge tag hints', 'https-redirection' ) ?></a>
            <div class="ehssl-tags-table-cont hidden">
                <table class="ehssl-tags-hint widefat striped">
                    <tbody>
                    <tr>
                        <td class="ehssl-tag-name"><b>{label}</b></td>
                        <td class="ehssl-tag-descr"><?php _e('The SSL certificate label', 'https-redirection') ?></td>
                    </tr>
                    <tr>
                        <td class="ehssl-tag-name"><b>{issuer}</b></td>
                        <td class="ehssl-tag-descr"><?php _e('The issuer of SSL certificate', 'https-redirection') ?></td>
                    </tr>
                    <tr>
                        <td class="ehssl-tag-name"><b>{issue_date}</b></td>
                        <td class="ehssl-tag-descr"><?php _e('The issuing date of SSL certificate.', 'https-redirection') ?></td>
                    </tr>
                    <tr>
                        <td class="ehssl-tag-name"><b>{issue_time}</b></td>
                        <td class="ehssl-tag-descr"><?php _e('The issuing time of SSL certificate.', 'https-redirection') ?></td>
                    </tr>
                    <tr>
                        <td class="ehssl-tag-name"><b>{issue_datetime}</b></td>
                        <td class="ehssl-tag-descr"><?php _e('The issuing datetime of SSL certificate.', 'https-redirection') ?></td>
                    </tr>
                    <tr>
                        <td class="ehssl-tag-name"><b>{expiry_date}</b></td>
                        <td class="ehssl-tag-descr"><?php _e('The expiry date of SSL certificate.', 'https-redirection') ?></td>
                    </tr>
                    <tr>
                        <td class="ehssl-tag-name"><b>{expiry_time}</b></td>
                        <td class="ehssl-tag-descr"><?php _e('The expiry time of SSL certificate.', 'https-redirection') ?></td>
                    </tr>
                    <tr>
                        <td class="ehssl-tag-name"><b>{expiry_datetime}</b></td>
                        <td class="ehssl-tag-descr"><?php _e('The expiry datetime of SSL certificate.', 'https-redirection') ?></td>
                    </tr>
                    <tr>
                        <td class="ehssl-tag-name"><b>{status}</b></td>
                        <td class="ehssl-tag-descr"><?php _e('The current status of SSL certificate.', 'https-redirection') ?></td>
                    </tr>
                    </tbody>
                </table>
            </div>
        </div>
                <?php
                return ob_get_clean();
        }
}