check a domain's SPF (Sender Policy Framework) record, löst includes gleich mit auf | include:_spf.example.com = TXT-DNS-record von _spf-subdomain (dig ... txt) | SPF-Test mit gutem Log (redirect...) http://vamsoft.com/support/tools/spf-policy-tester
DNS-based block list information/database. Resource to find out information on DNS block lists and check IPs to see if the are block listed in over 100 blacklist in just seconds.