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SPF generator
Build an SPF record and count its lookups.
What this does
Builds an SPF TXT record from the servers that send mail for your domain, and counts the DNS lookups it will cost.
The 10-lookup limit
SPF allows at most 10 DNS lookups when a receiving server checks your record — a, mx and each include: count as one each. Go over 10 and SPF returns PermError, which most receivers treat as a fail, for mail that would otherwise have passed.
Choosing the all mechanism
-all tells receivers to reject anything not listed. ~all asks them to mark it suspicious instead. +all authorizes every server on the internet to send as your domain, which defeats the point of SPF — this tool warns if you pick it.