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ZeroHook | SecurityTools

What should I do

Fix 421 4.7.28

This is a rate limit, not a missing record. Google's row sends you to the bulk sender guidelines.

  • Read which 421 4.7.28 text you got. The first row is an unusual rate of email. Other rows name an IP, a netblock, a DKIM domain, an SPF domain, a URL, or a repeated Message-ID.
  • The list last updated 18 September 2026 UTC does not name a DNS change for this status.