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Resolving SPF Records

SPF (Sender Policy Framework) is a mechanism to improve email delivery by specifying which hosts are permitted to send email claiming to be from a particular domain. The SPF record on a domain is a TXT value which begins v=spf1 and contains various syntax which eventually resolves a series of addresses.

Part of the syntax can be include:<fully-qualified-domain> which is a pointer to another record containing further addresses. This is often used to provide a single reference that domain name administrators can use to reference third-party email hosts without needing to update it whenever the third-party service updates their systems. For example, the reference for Office 365 is, for Gmail it is and Mailchimp is

When troubleshooting mail delivery it may be necessary to expand this syntax to IP addresses. This can be done as follows:

Open a command prompt and enter:

nslookup -q=TXT <domain>

This command fetches the TXT records for <domain> using Google DNS ( Look for any TXT records starting with v=spf1. If those lines contain include:<DNS> syntax, issue a new command to expand this value:

nslookup -q=TXT <DNS>

Continue this process until the TXT records no longer contain include: commands.

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