SPF Include Limit Calculator

SPF RecordEmail AuthenticationDNS LookupsSPF FlatteningDMARC

SPF Include Limit Calculator

The SPF specification limits records to 10 DNS lookups. Exceeding this causes PermError — effectively breaking SPF for your domain.

Known Sending Services / Includes

Google Workspace (include:_spf.google.com)

Microsoft 365 (include:spf.protection.outlook.com)

Mailchimp (include:servers.mcsv.net)

Salesforce Marketing Cloud

HubSpot (include:_spf.hubspot.com)

SendGrid (include:sendgrid.net)

Zendesk

Additional custom includes Each include typically uses 1 lookup

The SPF 10-Lookup Rule

RFC 7208 limits SPF records to 10 DNS-resolving mechanisms. Exceeding this returns PermError, which many receivers treat as SPF failure — breaking email authentication for your entire domain.

Each include:, a:, mx:, and redirect= costs one lookup. Nested includes in third-party records count against your limit too.

SPF flattening: Tools like dmarcian or AutoSPF expand includes to raw IP ranges, eliminating lookup costs
DKIM as backup: DKIM alignment in DMARC means SPF failure alone may not block delivery if DKIM passes

SPF Include Limit Calculator

SPF Include Limit Calculator

The SPF 10-Lookup Rule

Related Calculators

INFRASTRUCTURE

OPERATIONAL NOTES

The Hidden Cost of Retry Pressure in High-Volume SMTP Systems

Inbox Placement Is a Lagging Indicator

What Breaks First When Volume Increases Too Fast

Why Shared IP Pools Fail at Scale

Separating Cold, Bulk, and Transactional Traffic at the Infrastructure Level

When NOT to Warm an IP

Contact Us