Study of 288 Cloud IPs Finds 4.5% Blocklisted and Uneven Reverse DNS Coverage
A developer sampled 288 IP addresses from AWS, GCP, and Cloudflare's publicly published ranges to assess their reputation across four metrics: reverse DNS, mail blocklists, BGP announcements, and RDAP records. All 123 GCP IPs had valid PTR records, roughly half of AWS IPs did, while only one of 15 Cloudflare IPs carried a reverse DNS entry, reflecting those ranges' proxy-focused purpose. Thirteen of the 288 IPs — about 4.5% — appeared on at least one public mail blocklist, with Cloudflare's small sample showing the highest rate at 33%. BGP data revealed that some IPs within AWS-published ranges are actually announced by third-party networks, including Verizon Business and YouTube's Irish AS, due to customers bringing their own IP space. The author notes the true blocklist rate is likely higher since Spamhaus, one of the most authoritative sources, could not be queried in this setup.
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