Email open rate dropped? How to find the change behind it

Why did my email open rate drop?

An email open rate drops for one of three reasons: fewer emails reached the inbox, fewer people chose to open them, or the way opens are counted changed. Each one points to a different kind of change, so the first job is to work out which of the three you are looking at.

• Delivery changes: a new sending domain or email platform, a DNS move that dropped an SPF or DKIM record, a DMARC policy edit, a sudden jump in volume or a rising spam complaint rate. Mail lands in spam, and mail in the spam folder is rarely opened.
• Audience changes: a new list import, a wider segment, a change to the rule that removes inactive contacts, or a new sign-up source with lower intent.
• Message changes: a new sender name, subject line style, preheader, template or send time.
• Measurement changes: bot filtering switched on, Apple Mail Privacy Protection opens excluded from reports, or a different tracking setup after a platform migration.

Most teams start with the subject line. A sharp drop from one send to the next, though, usually points to something that changed outside the copy: delivery, audience or measurement. A slow slide over several months points more to list fatigue and a gradual shift in who is on the list.

Is the drop real, or did the way opens are counted change?

Check measurement before anything else. Open tracking relies on a tiny image that loads when the email is displayed, and several features load that image without a person reading the email.

Apple says Mail Privacy Protection downloads remote content in the background by default, regardless of whether you engage with the email. Mailchimp says this produces inflated and inaccurate open rates, and lets you tick a box to exclude these opens from reports for emails sent on or after June 22, 2024. Security scanners do something similar: Mailchimp notes they often open emails and click links before your contacts do, and that open and click metrics will drop significantly when bot filtering is turned on.

So a drop can appear with no change in real reading at all. Compare these signals before you blame the content:

If clicks held steady while opens fell, log the reporting change with its date and move on. Mailchimp itself recommends focusing on clicks, which it says are not affected by Apple MPP.

Which sender changes push emails into spam?

Mailbox providers decide inbox placement partly on authentication and complaints, and both depend on changes your team or a vendor makes. Since February 1, 2024, Gmail requires every sender to set up SPF or DKIM, keep valid forward and reverse DNS records, use TLS and keep the spam rate reported in Postmaster Tools below 0.3%. Senders of 5,000 or more messages a day to Gmail must also set up SPF, DKIM and DMARC, align the From: domain with the SPF or DKIM domain, and support one-click unsubscribe (Gmail sender guidelines). Google recommends staying below 0.10%.

Yahoo asks bulk senders for SPF and DKIM, a DMARC policy of at least p=none, one-click unsubscribe honoured within 2 days and a spam rate below 0.3%, calculated on mail delivered to the inbox (Yahoo sender best practices).

The changes that most often break these rules are ordinary ones:

• Moving the domain to a new DNS provider without copying the SPF, DKIM and DMARC records.
• Adding a new tool that sends from your domain (a CRM, a help desk, a booking system) without authorising it.
• Switching email platform or sending domain, so mail goes out from a setup with no sending history.
• Tightening DMARC from p=none to quarantine or reject before every sender passes.
• Removing or hiding the unsubscribe link, which pushes people to the spam button.
• Importing an old list, or doubling send volume overnight.

Each of these has a date. Once you know the date, you can compare it with the first send that dropped.

Where can I see what changed in deliverability?

Start with Google Postmaster Tools if you send to Gmail addresses, then your email platform's reports, then your DNS and website change records.

• Postmaster Tools: the "Compliance status" dashboard marks each Gmail requirement as compliant or needing work, "Spam rate" shows the share of authenticated mail that users reported as spam, and "Authentication", "Delivery errors" and the reputation dashboards show failures and rejections. Data is in UTC, usually updates within 24 hours and can be viewed for the last 7 to 120 days (Postmaster Tools dashboards).
• Email platform reports: opens, clicks, bounces, spam complaints and unsubscribes per send, split by mailbox provider when your platform offers it. Check the account settings for bot filtering or MPP exclusions too.
• DNS and domain records: your DNS provider's change history, or the ticket of whoever moved the domain.
• Team changes: list imports, segment rules, new templates, new sender names. These usually live only in people's heads or in chat threads.

Keep in mind one limit Google states: the spam rate dashboard only counts messages users mark as spam by hand. Mail that Gmail routes to spam on its own does not count, so a low spam rate can still hide a placement problem.

How do I isolate which change caused the open rate drop?

Isolate the cause by putting every change from the two weeks before the first bad send on one timeline, then testing the most likely one first.

1. Rule out reporting changes
2. Check authentication and spam rate
3. Line up every change
4. Test one hypothesis

Write down the date and time of the first send that dropped. Then collect every change before it: DNS and domain edits, new sending tools, platform settings, list imports and segment rules, template and sender name changes, and send time. Mark which ones touch delivery, which touch audience and which touch measurement, and check whether the drop is concentrated at one mailbox provider.

With every change on one timeline, the answer is often visible at a glance: you would see that the DNS move happened days before the first bad send, and that Gmail authentication failures started right after it. That is the job of a marketing change log, and you can keep one per client in Changeline, where the team logs email, website and tracking changes with date, owner and reason.

To confirm, fix the most likely cause and watch the next send. If DKIM was missing, restore it, check that Postmaster Tools shows authentication recovering, and compare the next send's open rate with the same segment before the change. Change one thing at a time, or you will not know which fix worked.

Example: A client asks: "Why did our newsletter open rate fall from 41% to 29% on Tuesday?" The agency lines up the changes. On Thursday the client's developer moved the domain to a new DNS provider. On Monday the team launched a new template. The drop is almost entirely in Gmail, and Postmaster Tools shows DKIM failures from Friday: the DKIM record had not been copied. Once it was restored, the next send recovered. The template was not the cause.

What should I fix first, and how do I explain it to a client?

Fix delivery problems first, because they affect every send, then audience, then content. Explain the drop with dates and evidence, not guesses.

When you report it, name the change, its date, the evidence and the fix: "DKIM stopped passing after the DNS move on Thursday, Gmail opens fell on the next send, and we restored the record on Wednesday." The guide to explaining a drop to a client has a structure you can reuse, and a change log template makes the next incident shorter. If you tag email links with UTMs, keep the naming stable too, or the drop will also look like a traffic change in analytics; see our UTM naming convention.

Then add one rule to your process: any change to the domain, DNS or sending tools is logged before it goes live, and someone checks authentication on the next send.