SPF flattening is primarily needed when an SPF record exceeds the 10 DNS lookup limit due to numerous includes, often from third-party services. However, correct SPF configuration, subdomain management, and focusing solely on return paths can mitigate the need. Validation involves checking the 'Received-SPF' header, using tools like `dig`, `nslookup`, online SPF checkers, and analyzing DMARC reports. While flattening addresses lookup limits, simplifying records, subdomain strategies, and a DMARC 'reject' policy are recommended alternatives to avoid management complexities and improve email deliverability. Improper SPF setup can lead to emails being marked as spam.
7 marketer opinions
SPF flattening is primarily needed when an SPF record exceeds the limit of 10 DNS lookups due to numerous 'include' statements for third-party senders. Validation involves verifying the SPF record's syntax and lookup count using tools like online checkers, `dig`, or DMARC reports. While flattening can resolve lookup issues, simplifying SPF records and exploring subdomain strategies are recommended alternatives to avoid management complexities. Incorrect SPF setup can lead to deliverability issues, including emails being marked as spam.
Marketer view
Email marketer from MXToolbox shares that SPF flattening should be used as a last resort. Where possible investigate a subdomain solution so messages from third party providers use different SPF records.
16 Aug 2023 - MXToolbox
Marketer view
Email marketer from StackExchange answers that not setting up SPF correctly or exceeding the limits can lead to emails being marked as spam, potentially damaging sender reputation and affecting email deliverability. SPF flattens helps minimize the risks.
4 Jan 2024 - StackExchange
3 expert opinions
SPF flattening might not be needed if SPF is correctly configured with better subdomain management. Focus on ensuring SPF records only include services using the apex domain's return path. Tools like `dig`, `nslookup`, and online SPF checkers can validate SPF records and confirm they adhere to the DNS lookup limit.
Expert view
Expert from Email Geeks explains that if SPF is configured correctly, SPF flattening might not be necessary, and better subdomain management might be a better solution.
27 Jan 2023 - Email Geeks
Expert view
Expert from Email Geeks explains that different services typically use different return paths, and SPF records are only needed for the return path, not any other domain. He advises to check the return path of mail sent by each service and only include services using the apex domain in the SPF record.
4 Dec 2023 - Email Geeks
4 technical articles
SPF flattening becomes necessary when a domain exceeds the 10 DNS lookup limit within its SPF record, especially due to numerous third-party services. Validation involves checking the 'Received-SPF' header to verify sending server authorization. It's advisable to avoid SPF flattening by implementing a DMARC policy of reject to block messages from invalid sources entirely.
Technical article
Documentation from Google Workspace Admin Help explains that SPF records have a limit of 10 DNS lookups. If this limit is exceeded, SPF flattening may be needed or the SPF record will fail, causing deliverability issues.
5 Oct 2023 - Google Workspace Admin Help
Technical article
Documentation from Microsoft indicates that SPF flattening becomes essential to maintain email deliverability when a domain utilizes numerous third-party services for sending emails, leading to exceeding the DNS lookup limit within the SPF record.
12 May 2025 - Microsoft
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