I want to train my SpamAssasin filter, and I've downloaded all SPAM tars from January 2015 to November 2015 from that site: untroubled.org/spam/
Also, I've downloaded my ham and SPAM emails from my personal gmail account. But my whole ham mails from gmail has about 2500 emails, while these 11 tars from untroubled.org contains about 410000 mails. So, the ham/spam relationship is about 1:160 and thus the SpamAssassin filter will be too much SPAM biased.
On the other hand, that kind of SPAM data set sites are thought mainly for SPAM researchers, not for system administrators.
So, my question is, what is what system administration usually do, or, what are the recommended practice? Do they use these kind of data sets? Is it that dangerous?