Server configuration mistakes

This is a list of problems related to server configuration problems when running OG Mailinglist.

Drupal files belong to nonexistent user

postfix/sendmail[2802]: fatal: no login name found for user ID 6226

For some reason, the drupal install. directory and all children were owned by user 6226 from group 6226. The problem went away once I changed the ownership.

chown -R www-data:www-data /var/www/drupal

Thank you, sano, for this tip.