What causes SPF authentication to fluctuate between 100% and 0% in Google Postmaster Tools?

Email marketer from Reddit shares that using a shared IP address can cause SPF fluctuations because the reputation of other senders on the same IP can impact your SPF results. Another user also stated that inconsistent sending volumes may also affect the reputation score.

Email marketer from Mailjet.com shares that regularly checking your SPF record for accuracy is crucial. Using SPF record checker tools can help identify and correct any errors that may be causing intermittent failures.

Email marketer from Mailhardener.com explains that temporary DNS errors can cause SPF checks to fail intermittently. These errors can result in fluctuations in SPF authentication results.

Email marketer from Postmarkapp.com shares that if you're using third-party senders, ensure their IPs are included in your SPF record. If these services aren't consistently sending or their IPs change without updating your SPF record, it can lead to SPF fluctuations.

Email marketer from SendGrid shares that if DMARC is set to reject emails that fail SPF, fluctuations in SPF can directly impact deliverability. If SPF sometimes passes and sometimes fails, you'll see inconsistent delivery rates.

Email marketer from GlockApps.com shares that fluctuations in SPF alignment are important. Ensure that the domain used in the 'MAIL FROM' matches the domain used for authentication to improve consistency.

Marketer from Email Geeks mentions that small volume days can cause weird fluctuations in GPT data. Also suggests if you're on your top-level domain, this is all much more difficult. DMARC point is good, but this is a solid reason to be on a subdomain for _marketing_ email sends.

Email marketer from StackExchange explains that exceeding the SPF record lookup limit (10 DNS lookups) can cause SPF to fail. If emails sometimes exceed the limit due to varying network conditions or email paths, this can lead to fluctuations in SPF results.

Marketer from Email Geeks explains that Google Postmaster Tools information could be about all other cases of email streams that are related to the domain, even if the domain is authenticated for the ESP but not for another service. As Ken pointed out, checking DMARC reports could help.

Email marketer from EasyDMARC.com explains that email forwarding can often break SPF. Understanding how forwarding impacts SPF checks is essential for preventing authentication failures. They recommend using SRS (Sender Rewriting Scheme).

Marketer from Email Geeks explains that bulk sends from something which isn't passing an SPF test will often cause that fluctuation on Google Postmaster Tools. Suggests checking DMARC reports.

Email marketer from Valimail.com explains that SPF failures can occur if emails are forwarded. Forwarding changes the IP address of the sender, causing the SPF check to fail unless SPF records are properly configured to account for forwarding.

Expert from Word to the Wise shares that email forwarding often causes SPF to fail because the original sender's IP no longer matches the sending server. If forwarding is common for your emails, it's critical to implement Sender Rewriting Scheme (SRS) or similar mechanisms to maintain SPF authentication.

Expert from Email Geeks explains that at least one of the email sources is not in the SPF record and this is unrelated to DMARC (although DMARC reports will be able to tell you which sources of email are failing SPF and why the DKIM signature is passing but DMARC is failing).

Expert from Spam Resource explains that inconsistent email sending practices, such as using different sending IPs or services without updating the SPF record, can lead to SPF authentication fluctuations. It also suggests ensuring that all authorized sending sources are accurately listed in the SPF record.

Documentation from DMARC.org explains that DMARC failures related to SPF can be caused by a number of reasons, including the SPF record not being properly configured to include all sending sources, or the use of third-party senders who are not authorized in the SPF record.

Documentation from RFC Editor specifies that syntax errors in the SPF record can cause the SPF check to fail. These errors can lead to inconsistent authentication results if they are intermittently triggered.

Documentation from AWS shares that if you are sending emails from AWS, you should make sure to include the regional endpoints in your SPF records to pass authentication checks consistently.

Documentation from Google Workspace Admin Help explains that SPF alignment requires that the domain used in the 'MAIL FROM' address (also known as the envelope sender address) matches the domain used to authenticate the email. Fluctuations could be caused by inconsistencies in this alignment.

Documentation from Microsoft explains that maintaining an up-to-date SPF record that accurately reflects all sending sources is critical. Outdated or incomplete SPF records can lead to SPF failures.