Authentication
What is SPF Flattening?
Replacing the include mechanisms in an SPF record with resolved IP addresses to stay under the DNS lookup limit.
SPF flattening rewrites an SPF record so that nested include, a, mx, and redirect mechanisms, which each cost DNS lookups, are expanded into the literal ip4 and ip6 ranges they resolve to. This keeps the record within SPF's hard limit of 10 DNS lookups, beyond which evaluation returns a permerror and SPF effectively fails. Because the underlying provider IPs change over time, a flattened record must be monitored and re-flattened automatically or it goes stale and starts failing legitimate mail.
Why it matters for cold email
Cold-email stacks that chain a sending platform, a mailbox provider, and a tracking domain often blow past the 10-lookup SPF limit, causing a permerror that breaks SPF and its DMARC alignment. Flattening fixes the lookup count, but a stale flattened record can silently authorize the wrong IPs or reject your own, so it must be maintained carefully.
Related terms
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