Use talosintelligence.com/reputation_c... to get a gut check on the reputation of an email sender (what I use most), IP address, or a file. Helpful to see if a sender is on spam blocklists, or see factors that affect mail deliverability.

Use ipinfo.io to see location and owner data for IP addresses, really useful in enriching data you get while investigating incidents. This one is freemium--you get basic stuff free/anon, signing up gets you a few more fields and API access, and paid plans gets bulk API use.

Trusted IP Data Provider, from IPv6 to IPv4

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