The Connection

Broken email infrastructure — specifically SMTP misconfiguration — causes form submissions to fail silently, which means Google Ads conversion tracking records zero conversions not because the tracking is wrong, but because the form never completed; the ads team diagnoses a tracking problem while the root cause is an email delivery problem.

Why This Matters

The standard Google Ads troubleshooting sequence (Website → GTM → GA4 → Google Ads) assumes the form submission itself succeeded. If SMTP is broken, the form fires the thank-you redirect or conversion pixel but the lead is lost — or in some configurations, the form does not complete at all, and neither the pixel nor the lead fires. An ads team following the four-step diagnostic will exhaust every tracking hypothesis and find nothing wrong, because nothing in the tracking stack is wrong. The fault lives one layer below where ads practitioners typically look. This means zero-conversion accounts may be misdiagnosed as bid strategy or tracking failures when they are email infrastructure failures.

Evidence

From ^[1]:
- From the Conversion Tracking section: "broken SMTP configuration causes form submissions to fail silently before they ever reach the client" — cited as a technical failure mode that compounds conversion tracking problems beyond simple misconfiguration ^[2].
- INEX spent $3,835 over ten months with zero recorded conversions; Aviary ran at ~$33/day with zero recorded conversions — both diagnosed as tracking configuration errors, but the SMTP failure mode described at Cordwainer shows zero-conversion accounts have a third possible root cause that is not a tracking error at all.

From ^[3]:
- PHP mail() "is treated as spam by major providers and should be treated as a legacy failure mode, not a fallback" — the failure mode explicitly called out is that PHP mail() does not deliver reliably, meaning form-submission emails (confirmations, notifications) sent via PHP mail() will silently disappear ^[4].
- The infrastructure section establishes that email delivery failures are invisible to the sender: high-bounce campaigns damage domain reputation without the sender knowing until deliverability degrades — the same invisibility pattern that makes SMTP failures hard to detect from the ads side.

Together:
- The email marketing article establishes that misconfigured or legacy sending infrastructure (PHP mail(), broken SMTP) fails silently and invisibly. The Google Ads article establishes that silent form failures are a confirmed conversion tracking failure mode at Cordwainer. Neither article states that an ads practitioner diagnosing zero conversions should check SMTP configuration as a first-order hypothesis — but together they make exactly that case.

Implication

When a Google Ads account shows zero or near-zero conversions and the four-step diagnostic (Website → GTM → GA4 → Google Ads) finds no misconfiguration, add a fifth step before declaring the tracking clean: submit a test form and verify that the form-confirmation email is received, that the backend notification email reaches the client, and that the sending method is not PHP mail(). If any of those checks fail, the conversion gap is an email infrastructure problem, not an ads problem. This check should be added to the standard account audit checklist and run before any bid strategy changes, because changing from Maximize Conversions to Maximize Clicks to compensate for zero conversions will not fix a broken contact form.

Questions This Raises

1. In accounts where zero conversions were eventually traced to SMTP or PHP mail() failures (e.g., Cordwainer), how many days of ad spend elapsed between campaign launch and root cause identification — and would a day-one form submission test have caught it immediately?
2. Does WP Rocket's caching plugin (already identified as a GCLID registration problem) also interfere with form submission processing in ways that could produce the same silent failure as broken SMTP, and have both failure modes appeared in the same account simultaneously?
3. When secondary sending domains are configured for bulk email (the portfolio standard), does the SMTP configuration for transactional/form-notification email on the primary domain ever get inadvertently broken during DNS changes for the secondary domain setup — making domain strategy changes a trigger for ads conversion drops?