Sender Policy Framework (SPF) specifies who is allowed to send email from your domain. A broken SPF record guarantees the spam folder.
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The Authorization Checklist
SPF is essentially a public list of IPs and services that are allowed to send email for you. If a sender isn't on the list, their email is rejected.
SPF records are strict. A single typo invalidates the entire record. We check for common syntax errors and typos.
You only get 10 DNS lookups per SPF check. Exceeding this makes your record invalid. We count them for you.
Ensure your IP ranges are correctly formatted (CIDR notation) and actually point to the servers you intend to authorize.