If the /var/www/html/squirrelmail path does not exist (directory or link, doesn't matter), then the backup/restore won't happy for the SquirrelMail data. This extra check was added to prevent errors for backing up things if the server doesn't have SM installed. The path check will use an internal cache method, so a new lstat is not run for each User. The dataskq would store it in the backup. The directadmin processes should also be safe from cache issues because the parent doesn't call this check, and each chiled is forked. (in case you delete the /var/www/html/squirrelmail path, but DA still thinks it's there).. but even if you have issues, just restart DA.