RFC 7208 limits an SPF record to 10 DNS lookups. Flattening replaces include: chains with their resolved ip4/ip6 ranges so you stay under the cap. Counts current lookups + builds the flat version.
Format: host: cidr1, cidr2. Use `dig +short txt _spf.host` to fetch and resolve each include.
v=spf1 ip4:35.190.247.0/22 ip4:64.233.160.0/19 ip4:66.102.0.0/20 ip4:23.253.182.0/24 ip4:50.56.21.176/28 ip4:40.92.0.0/15 ip4:40.107.0.0/16 ~all