As in the title, what is the maximum value to which crawl-delay can be set in robots.txt?
I get very few hits from bing but bing consumes much more resources than google in my server.
So I do not want to block bing at all (because it's not nice) but I need to limit the bing access to my server.
I saw someone use crawl-delay: 120, but then I read that maybe bing understand only crawl-delay from 10 to 30.
I did some tests on my robots.txt, initially it seems to work, but after a while I start to get a lot of requests from bing. I also tried to set the scan frequency on bing webmaster tools, but it did not change much.
The same thing I would like to do for yandex, I can not receive 250000 hits a day in exchange for ten visits a month, but I do not want to block it completely.
To summarize, what are the maximum crawl-delay values that can be used for bing and yandex?