uninstall.php

<?php
/**
 * WP PGP Encrypted Emails uninstaller.
 *
 * @link https://developer.wordpress.org/plugins/the-basics/uninstall-methods/#uninstall-php
 *
 * @license https://www.gnu.org/licenses/gpl-3.0.en.html
 *
 * @package WordPress\Plugin\WP_PGP_Encrypted_Emails\Uninstaller
 */

// Don't execute any uninstall code unless WordPress core requests it.
if ( ! defined( 'WP_UNINSTALL_PLUGIN' ) ) { exit(); }

require_once plugin_dir_path( __FILE__ ) . 'wp-pgp-encrypted-emails.php';

$meta_keys = array(
    WP_PGP_Encrypted_Emails::meta_key,
    WP_PGP_Encrypted_Emails::meta_smime_certificate,
    WP_PGP_Encrypted_Emails::meta_encryption_method,
    WP_PGP_Encrypted_Emails::meta_key_empty_subject_line,
    WP_PGP_Encrypted_Emails::meta_key_sign_for_unknown_recipients,
    WP_PGP_Encrypted_emails::meta_key_receive_signed_email,
);
if ( get_option( WP_PGP_Encrypted_Emails::meta_key_purge_all ) ) {
    $meta_keys[] = WP_PGP_Encrypted_Emails::meta_keypair;
    $meta_keys[] = WP_PGP_Encrypted_Emails::meta_key_purge_all;
}

foreach ( $meta_keys as $name ) {
    delete_option( $name );
    delete_metadata( 'user', null, $name, null, true );
}