If you get the message "Documents contains no data" (message depends on browser) in a Squirrelmail deployment, it is probably Apache's configuration.
To fix this, comment out the line containing LimitRequestBody in /etc/httpd/conf.d/php.conf and it should work after restarting httpd.
Also, check for memory_limit, post_max_size, and upload_max_filesize in /etc/php.ini
