dj_discourse_sso/Configuration/TCA/Overrides/fe_users.php

<?php
defined('TYPO3_MODE') or die();

// Modifications on existing columns:
if ($GLOBALS['TCA']['fe_users']['columns']['email']['config']['size'] < 40) {
    $GLOBALS['TCA']['fe_users']['columns']['email']['config']['size'] = 255;
}