To figure out whether it’s your SPF setup or your email provider’s reputation/configuration, look at it in this order:

1) Check the email headers of a message that landed in spam

Open the spam email and view the full headers / message source. Look for:

• SPF: pass or fail
• DKIM: pass or fail
• DMARC: pass or fail
• Any notes from Gmail/Outlook/Yahoo like:
  • spf=pass
  • dkim=pass
  • dmarc=pass
  • sender authentication failed
  • bulk sender, suspicious, phishing, etc.

What this tells you

• SPF fail → likely a DNS/authorization issue.
• SPF pass but still spam → SPF is probably not the main problem.
• SPF pass, DKIM pass, DMARC fail → alignment/policy issue.
• All pass but still spam → more likely provider reputation, content, or domain/IP history.

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2) Verify SPF independently

Check your domain’s SPF record in DNS. It should:

• Exist as a single TXT record for the domain
• End with ~all or -all depending on your policy
• Include the mail provider’s sending hosts

Common SPF problems

• Multiple SPF records on the same domain
• Missing the provider’s include: entry
• Exceeding the 10 DNS lookup limit
• Sending mail from a service not listed in SPF
• Using the wrong domain/subdomain in the Return-Path or From domain

If you use a third-party transactional provider, their docs usually give the exact SPF include to add.

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3) Check whether the provider is the issue

If SPF/DKIM/DMARC all pass, the next suspects are usually:

• Shared IP reputation (if they send from shared infrastructure)
• Dedicated IP reputation (if you use one)
• Domain reputation based on complaint/engagement history
• Content patterns that trigger filters
• Missing or weak DKIM signing
• Poor list hygiene or lots of bounces/complaints
• Inconsistent sending volume or sudden spikes

Signs it’s the provider/reputation

• Headers show authentication passed
• Spam placement varies by mailbox provider (Gmail vs Outlook vs Yahoo)
• Delivery is good for some recipients but not others
• Messages started landing in spam after a volume spike or provider change

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4) Use a seed test

Send the same message to test accounts at:

• Gmail
• Outlook/Hotmail
• Yahoo
• iCloud

Then compare:

• Inbox vs spam
• Authentication results in headers
• Whether all providers behave the same

If Gmail and Outlook both spam it, that points more to reputation/content/authentication than one mailbox provider.

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5) Check DMARC reports if you have them

If you’ve set up DMARC, aggregate reports can show:

• Which systems are sending mail for your domain
• Whether SPF/DKIM align
• Where failures happen

This is one of the fastest ways to see if your provider is sending correctly.

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6) Confirm alignment

Even if SPF passes, DMARC cares about alignment:

• The domain in the visible From: address must align with the SPF-authenticated domain and/or DKIM signing domain.

Example:

• From: billing@yourdomain.com
• SPF authenticates mail.provider.com
• If it’s not aligned with yourdomain.com, DMARC can fail even though SPF says pass.

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7) Check blacklists and reputation tools

Use tools like:

• MXToolbox
• Google Postmaster Tools
• Microsoft SNDS
• SenderScore / other reputation tools

These can show whether:

• Your IP/domain is blacklisted
• Reputation is poor at major mailbox providers
• The provider’s IP pool is the problem

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Quick rule of thumb

• SPF fail in headers → fix SPF/authentication.
• SPF pass, DKIM pass, DMARC pass, but spam persists → likely provider reputation, IP reputation, or content.
• DMARC fail → likely alignment or configuration issue, even if SPF passes.

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If you want, paste a redacted copy of the email headers here (remove personal info), and I can help you interpret whether it’s SPF, DKIM, DMARC, or provider reputation.