How to Improve Cold Email Open Rates

Cold email open rates depend on inbox placement first. An email that lands in spam is rarely seen, however good its subject line. Once the email is in the inbox, three lines decide whether it gets opened: the sender name, the subject line and the preview text.

The open rate itself is a weak metric for cold email. It is counted by a tracking image that privacy features load on the reader's behalf and that blocked images never load, and Google says low open rates are not a reliable sign of spam placement. Fix placement, then the three lines the reader sees, and judge the campaign by replies.

We make Outreach2day, cold email infrastructure with domains, mailboxes, warmup and campaigns. Where a step below uses one of our features, we say so.

What an Open Rate Measures and Why It Misleads

Sending tools count an open when a tracking pixel loads: a tiny, invisible image with a unique address, added to the HTML of each email. When the image is requested from the tool's server, the tool marks that recipient as opened. Open rate is unique opens divided by emails delivered.

Anything that loads the image without a person reading the email adds an open. Anything that stops the image from loading removes one.

Apple Mail Privacy Protection

Apple describes Mail Privacy Protection as a feature that "helps protect your privacy by preventing email senders from learning information about your Mail activity." Its Protect Mail Activity setting "downloads remote content in the background by default — regardless of whether you engage with the email" (Apple).

For a sender, every recipient who reads mail in Apple Mail with this setting on can show as opened whether or not they read the email. The share of such recipients differs from list to list, so the inflation differs too, and two campaigns to different lists can't be compared on opens.

Image Proxies

Gmail loads images through Google's servers: "When your users open email messages, Gmail uses Google's secure proxy servers to serve images that might be included in these messages" (Google Workspace Help). Gmail's help for users says senders "may know whether you've opened an email that has an image," and that they "can't use image loading to get information about your computer or location" (Gmail Help).

So an open from a Gmail reader tells you the image was requested through Google's servers, and nothing about the reader's device or location.

Blocked Images and Plain Text

When a reader or their company's mail settings block images, the pixel never loads and a read email counts as unopened. A plain-text email carries no pixel at all, so it has no open rate. We recommend plain text for cold email, for the reasons in the tracking section below.

What Google Says About Open Rates

Google's sender guidelines address opens directly (Google sender guidelines):

• "Google doesn't track open rates"

• "Google can't verify the accuracy of open rates reported by third parties"

• "Low open rates aren't necessarily an accurate indicator of deliverability or spam classification issues"

If you track opens at all, use them to compare two variants sent to the same list, from the same mailboxes, on the same days. Don't read a low open rate as proof of spam placement or a high one as proof of interest.

Fix Placement Before Copy

An email in the spam folder is rarely opened, so check placement before you rewrite the subject line. Copy can cause spam placement too; the paired test at the end of this section shows whether it does. Work through these in order.

Authenticate Every Sending Domain

Authentication proves to mailbox providers that mail from your domain comes from you. Google requires every sender to "Set up SPF or DKIM email authentication for your sending domains," and senders of more than 5,000 messages a day to set up SPF, DKIM and DMARC (Google sender guidelines). Set up all three on every cold domain at any volume.

Check a domain with the SPF, DKIM and DMARC checker. It reads the records in your browser, and each finding says what breaks and how to fix it.

Warm Up and Cap Volume

New mailboxes have no sending history. We recommend 14 days of warmup before the first cold email, full volume from day 14, and warmup running for as long as the mailbox sends cold email.

Keep each mailbox at up to 25 cold emails a day and each domain at up to 5 mailboxes. To send more, add mailboxes in batches and check the warmup inbox rate before each new batch.

Clean the List Before Every Send

Invalid addresses bounce, and a high bounce rate hurts your reputation. Verify addresses before each send and remove the ones that fail; our guide to email verification programs compares the tools.

Remove anyone who asks you to stop, and keep complaints low. Google asks senders to keep the spam rate "below 0.10%" and to "avoid ever reaching a spam rate of 0.30% or higher." A complaint costs more than a missed reply: it tells the provider the email was unwanted.

Keep the First Email Plain

Links, images and tracking pixels add content that filters judge. Google's Postmaster Tools help says: "Some types of message content, such as Internet links, increase the possibility of messages being treated as spam" (Postmaster Tools help).

Send the first email as plain text with no links, including the website in the signature. Mail apps turn a bare domain into a link. Paste each step into the cold email copy checker: it flags links, bare domains, images, spam-trigger phrases and fake Re: or Fwd: subjects before you send.

Test Placement With a Control Email

A placement test sends your email to seed inboxes at Google and Outlook and reports inbox or spam for each one. A single test is noisy, so pair it: send a neutral, non-sales email and your campaign email from the same mailboxes in the same minute.

Read Google and Outlook results separately: the same email can land in the inbox at one and in spam at the other. Repeat a result on a second day before you change domains or mailboxes. The full method is in our inbox placement test guide, and how reliable placement tests are explains the noise.

Outreach2day includes Google and Outlook placement tests for mailboxes that are 21+ days old, with up to 100 mailboxes per test and an inbox or spam result for each seed.

Sender Name, Subject Line and Preview Text

Once the email is in the inbox, the reader sees three things before opening it: the sender name, the subject line and the first words of the body. A cold email comes from someone the reader does not know, so all three should read like a normal message from one person to another.

Sender Name

Use the name of the person the email comes from, as in "Anna" or "Anna from Outreach2day". Keep it the same in every email from that mailbox and in the signature. A company name alone or a team name such as "Sales Team" reads like a newsletter.

Subject Line

What to aim for:

• Short and specific: the reader's company, role or a problem they are likely to have

• Written the way people write to colleagues, in sentence case

• A question when the email asks one

• A first email without "Re:" or "Fwd:": a fake reply prefix misleads the reader

What to leave out: ALL CAPS, several emojis, exclamation marks, and promises the email does not keep. These annoy readers and can trigger spam filters.

At volume, the same subject line can go out thousands of times a day. Write it as spintax, so few exact subjects repeat, and group the variations into a small number of families you can measure. The subject line spintax generator skill writes families in this format, and our cold email subject lines post has examples and patterns.

Send follow-ups with an empty subject so they stay in the same thread as the first email.

Preview Text

Email clients show the start of the body next to or under the subject. Marketing emails set it with hidden preheader text; in a plain-text cold email the preview is the first line of the body. Write that line for the inbox list:

• Start with the reason for the email: who it is for or what you noticed about their company

• Keep the greeting short ("Hi Sarah,") so the first sentence shows in the preview

• Avoid repeating the subject line word for word

Should You Track Opens in Cold Email?

We recommend turning open tracking off for cold email. Compare what each setup puts in the email and what it tells you:

The tracking image goes into every email, including the first one from a mailbox the recipient has never heard from, and the tracking domain's reputation becomes part of yours. In return you get an open rate with the gaps described above.

Send plain text with no pixel and no links in the first email, and share links after the prospect replies. What Google says about links and URL-domain rate limits is in do open tracking and links hurt deliverability.

What to Measure Instead

Replace opens with metrics that count what people and mail servers did.

Read them together:

• Replies fall while auto-replies hold: the emails are arriving, so look at the list, the offer and the copy

• Replies and auto-replies fall together: look at placement and run a paired test

• One mailbox's warmup inbox rate drops while the others hold: act on that mailbox and its domain first

• Cold bounces rise: check the list source and the verification step

To compare subject lines by replies, send each subject family from the same mailboxes to the same list segment over the same days. With the subject as the only difference, the gap in human replies is the subject's effect.

In Outreach2day, each mailbox shows its warmup inbox, spam and bounce rate for the last 14 days with a green, amber or red status. Incoming mail is split into human replies, out-of-office and bounces, and cold and warmup bounces are counted separately. Formulas for each rate are in email campaign performance metrics.

FAQ: Cold Email Open Rates

What Is a Good Cold Email Open Rate?

There is no benchmark you can rely on. The number depends on how many of your recipients use Apple Mail with Protect Mail Activity, how many block images, and whether you track opens at all. Email marketing benchmarks measure newsletters and promotions sent to subscribers, a different audience from cold email.

Compare your open rate only with your own earlier sends that used the same tracking settings, and judge campaigns by reply rate. Google says low open rates "aren't necessarily an accurate indicator of deliverability or spam classification issues," so a low number calls for a placement test before any conclusion.

Why Are My Cold Email Open Rates Low?

Check these in order:

1. Placement: run a paired placement test to Google and Outlook seed inboxes

2. Authentication: SPF, DKIM and DMARC on every sending domain

3. Mailbox readiness and volume: at least 14 days of warmup and up to 25 cold emails per mailbox a day

4. The list: bounces, outdated contacts and people outside your target market

5. The three lines the reader sees: sender name, subject line and preview text

6. Measurement: recipients who block images count as unopened, and plain-text emails have no opens to count

Does Open Tracking Hurt Deliverability?

It adds risk. Open tracking puts an image hosted on the tracking domain into every email, so that domain is part of every message filters scan and its reputation becomes part of yours. What you get back is an open rate that, in Google's words, isn't "necessarily an accurate indicator" of spam classification. We recommend sending cold email with open tracking off.

Is A/B Testing Subject Lines Worth It?

Yes, when the result is measured by replies. Send the variants from the same mailboxes to the same list segment over the same days, split the sends evenly, and compare human reply rates. Opens are a poor judge here, because Apple Mail's background downloads and blocked images change the count whatever the subject line says.

Small differences in replies are often noise. Run the winner against a new variant on the next send, and keep the subject that wins twice. Outreach2day sequences support up to four A/B variants and spintax.

Sources

Checked October 1, 2026:

• Apple: Mail Privacy Protection & Privacy: background download of remote content

• Google: Email sender guidelines: open rates, authentication, spam rate thresholds

• Google Workspace Help: Set up an image URL proxy allowlist: Gmail image proxy

• Gmail Help: Turn images on or off in Gmail: what image loading tells senders

• Gmail Help: Postmaster Tools dashboards: links and spam classification

Outreach2day sets up the domains, DNS records, mailboxes and warmup for cold email, with per-mailbox warmup stats and Google and Outlook placement tests, at $2.50 per mailbox a month.