Gmail Deliverability Troubleshooting Guide

The campaign is “delivered” in Klaviyo. A customer forwards a screenshot from Gmail’s spam folder. Yahoo looks normal. That is a Gmail problem, and your account-wide open rate will not explain it.

This is the troubleshooting order for that case. It is not a restatement of InboxEagle’s Gmail placement studies. Those stay on their own URLs: what a large set of Gmail-bound messages showed, Promotions versus spam, and the Q1 Gmail benchmark. Use them as evidence after you know which check failed. The spam diagnosis is the cross-provider version of the same first hour.

Last verified: 26 September 2026, against Google’s sender guidelines, the guidelines FAQ, and Postmaster Tools dashboards.

What Gmail is deciding

Gmail can do three different things with your mail. It can accept it and file it in Primary, Promotions, Updates, or spam, and your ESP counts a delivery in every one of those cases. It can defer it, a temporary failure your ESP may retry. Or it can reject it at Gmail’s SMTP servers. Starting November 2025, Google said it is ramping up enforcement on non-compliant traffic, and messages that fail the sender requirements will see disruptions, including temporary and permanent rejections. That does not mean every guideline miss becomes a bounce.

Inbox placement versus delivery rate is the metric split. If the customer never got a message and there is no Gmail spam screenshot, start with delivered but not received so you do not “fix Gmail” for a Smart Sending skip.

Requirements, guidelines, and the mitigation cutoff

Keep the labels straight. Google uses all three.

Postmaster Tools calculates spam rate as the percent of messages delivered to an engaged recipient’s inbox and then marked spam. Messages that went to spam and were marked “not spam” count toward inbox delivery in that calculation. The dashboard shows the rate for DKIM-authenticated mail to Gmail accounts. It is not your ESP’s complaint rate. Klaviyo’s documentation says Gmail does not provide spam complaints to ESPs. What 0.10% and 0.30% mean walks through the same figures in more detail.

Compliance status in Postmaster Tools is the checklist against these requirements. Google says that after you fix a failing row, it can take up to seven days to show the change. Google has said the Domain and IP Reputation dashboards will not move to Postmaster Tools v2 and will be retired. Do not build your monitoring around them; use v2’s Compliance Status and spam rate instead. Google has published no retirement date, and several vendors reported reputation data stopped appearing in August 2026. The Postmaster Tools guide is the screen-by-screen reference.

Gmail deliverability troubleshooting checklist

1. Confirm you are looking at Gmail spam, not Promotions, and not an Outlook 550 5.7.515.
2. In Postmaster Tools, open the domain that DKIM-signed the mail. Your root domain and mail.yourstore.com are different dashboards. Subdomain strategy explains why registering the wrong one hides the failing stream.
3. Read Compliance status line by line: authentication, alignment, DNS, TLS, format, spam rate, DMARC, one-click unsubscribe.
4. Read the spam-rate trend for the days of the bad sends. A single spike and a rate that has sat over 0.10% for two weeks are different repairs.
5. On a spam-folder copy, read Authentication-Results. Passing DNS in a checker and failing on the live message means a source is sending outside the records you checked.
6. Compare the audience with the last Gmail send that placed. Win-backs, full-list sales, and a welcome series that keeps writing to non-openers are the usual complaint source. Welcome series risk is the flow version.
7. Only then open the template. Authentication and complaints explain more sudden Gmail failures than a subject line.

Five of those seven checks happen before you touch the email itself. The order is a triage habit, not a Google rule, and if your spam-folder copy shows a content-level problem such as a broken link host, skip ahead.

What to change at Gmail

Compliance failures. Add the missing SPF include, turn on DKIM for that domain, or publish DMARC. SPF, DKIM, and DMARC is the setup page. One-click unsubscribe is a bulk marketing requirement: List-Unsubscribe and List-Unsubscribe-Post as described in RFC 8058. Google recommends honoring the request within 48 hours; RFC 8058 itself sets no deadline. The List-Unsubscribe header generator writes both headers. A visible footer link is not a substitute for the header.

Spam rate. Stop mailing the segment that produced the complaints. Suppress complainers. Do not import a fresh list to dilute the rate. Google says a high spam rate increases spam classification, and that improvement takes time to show up. If you are already over 0.30%, the FAQ’s mitigation window is seven consecutive days under 0.30%. That window is about support eligibility. It is not a date on which Gmail owes you the inbox.

Promotions, when spam is not the folder. Do not burn a DNS change on a tab. Decide whether Primary is actually required for that message. Receipts and lifecycle mail are the cases where a tab is costly. A weekly sale landing in Promotions can be normal category behavior.

A new sending domain or a new ESP. Gmail has no history for that domain. Warm it on people who already interact with your store. Changing the sending domain is the cutover, not a troubleshooting shortcut.

How to verify the Gmail fix

Send the next message to recent clickers, from the same domain you fixed.

• The received Gmail message shows SPF, DKIM, and DMARC pass.
• A seed mailbox at Gmail shows inbox or promotions, whichever you expected, and not spam. InboxEagle’s seed list includes Gmail, Yahoo, AOL and Outlook. Yahoo, AOL and Outlook tell you whether the problem was only Gmail.
• The next Postmaster spam-rate point is not higher than the send you just made. One clean test does not erase a week above 0.30%.

If recent clickers still land in spam after compliance is green, treat it as reputation and follow the first 24 hours of recovery. Do not launch a replacement domain the same day.

Gmail fixes that backfire

Do not use open rate as the Gmail verdict. Apple Mail Privacy Protection and spam-folder image loads both move that number. Do not buy addresses to “improve engagement.” And do not make unsubscribing harder: the spam button is the signal Postmaster Tools counts.

What to monitor at Gmail after the fix

Watch Gmail on your revenue mail: campaigns, cart, browse, welcome, and post-purchase, especially when two of those can hit one person the same day. Postmaster monitoring is the spam rate and compliance view. Placement at Gmail is the folder view. You want both, because a compliant domain can still be filed in spam, and a spam-folder problem can exist for days before you notice it in revenue.

Sources

• Email sender guidelines, Google.
• Email sender guidelines FAQ, Google. Mitigation ineligibility above 0.30%, and the seven-day return.
• Postmaster Tools dashboards, Google. Spam-rate definition and Compliance status.
• Email deliverability FAQs, Klaviyo. Gmail complaints are not returned to the ESP.