Password reset – Disabled for LDAP accounts

Code for checking and blocking LDAP users to reset password.

/**
 * Checks whether a user is LDAP user and restricts to reset password.
 *
 * @param  bool   $allow    Whether the password can be reset.
 * @param  int    $user_id  The ID of the user.
 * @return bool|WP_Error
 */
function ldap_restrict_password_reset( $allow, $user_id ) {

    $user = get_user_by( 'id', $user_id );
    if ( ! empty( $user ) ) {
        $user_login   = stripslashes( $user->data->user_login );
        $user_email   = stripslashes( $user->data->user_email );

        // check if the user a LDAP user
        if( $user_email === '[email protected]' ) {
            return new WP_Error('no_password_reset', __('Password reset is not allowed for this LDAP user on this site.'));
        }
    }

    return $allow;
}
/* Filters whether the user's password can be reset. */
add_filter( 'allow_password_reset', 'ldap_restrict_password_reset', 10, 2 );

Note: Please add code to get and check if the user is a LDAP user or not.

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These are some of the hooks that you can use to stop sending email and show error message.

/**
 * Fires before a new password is retrieved.
 *
 * @since 1.5.1
 *
 * @param string $user_login The user login name.
 */
do_action( 'retrieve_password', $user_login );

/**
 * Filter whether to allow a password to be reset.
 *
 * @since 2.7.0
 *
 * @param bool true           Whether to allow the password to be reset. Default true.
 * @param int  $user_data->ID The ID of the user attempting to reset a password.
 */
$allow = apply_filters( 'allow_password_reset', true, $user_data->ID );

if ( ! $allow )
    return new WP_Error('no_password_reset', __('Password reset is not allowed for this user'));
else if ( is_wp_error($allow) )
    return $allow;

Above is part of the code taken from wp-login.php file. http://wpseek.com/retrieve_password/