aggiorno ulteriormente:
nel frattempo ho dialogato ancora con l'assitenza Bing (via mail).
mi hanno chiesto di inviare loro:
almeno un file log (in modo da analizzare meglio la questione) il file robots.txtmi hanno risposto così:
We understand that our bots are overcrawling your website. We apologize for the inconvenience this issue has caused you.
To rectify the issue, please create a robots.txt file and upload it to your root directory, your robots.txt file should contain the following directive:
User-agent: bingbot
Crawl-Delay: 30
User-agent: msnbot
Crawl-Delay: 30
This is to set up a crawl delay for bingbot and msnbot. We also recommend adjusting the crawl frequency using Bing Webmaster Tools. You can set up which time is most suited for our bots to visit your website, you can select the hours when there is less requests of bandwidth from your site.
You may check this article http://www.bing.com/webmaster/help/crawl-control-55a30302 for more information.
I hope this information helps. Please let us know if you need further assistance.