What is the SPF 10-lookup limit and why does it exist?
The SPF lookup limit exists to prevent Denial of Service attacks that could be created through excessive DNS lookups. The standard defined in RFC 7208 caps the number of DNS querying mechanisms include a mx ptr and exists at ten per SPF check. If a record triggers an eleventh lookup the evaluation fails with a permerror. This cap protects receiving servers from unnecessary load and forces senders to design efficient SPF records.
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