An anonymous visitor has no email address. Email retargeting therefore only starts once the address has been captured on your site, through a signup form or a checkout step. It means emailing an identified person who left the site without buying or subscribing. The message depends on what they did: abandoned cart, product page viewed, form left unfinished.
Tracking relies on a pixel and cookies, and both Apple and Gmail limit what you can measure. Another point is rarely covered: an address typed into a website is often wrong, and emailing it costs you sender reputation.
What is the difference between email retargeting and remarketing?
Remarketing in advertising shows banners to a visitor recognized by a cookie, through an ad network such as Google Ads or Meta. Email retargeting goes through the inbox, with an email address as the key. The first targets anonymous audiences. The second requires an address and consent.
How does a site find the address of a visitor who left?
It only finds it if the visitor typed it on the site at some point. On the first visit, a tracking pixel or script sets a first-party cookie: an anonymous identifier tied to your domain that records pages viewed and items added to the cart. As long as the visitor gives nothing, that identifier has no name.
Visitor identification happens when they enter their address. Three entry points dominate: the discount pop-up, the shipping step of checkout and the click from a previous campaign. The tool then links the address to the cookie and attaches the whole browsing history to the contact record. That link lets you write “you left these sneakers in size 42” instead of a generic message.
A visitor can clear their cookies or switch devices before entering an address. The link then disappears and no follow-up is possible. Third-party cookies play no part in the mechanism: the identifier comes from your own data.
When should each follow-up go out?
For a cart, the Klaviyo help center recommends a first email 2 to 4 hours after checkout starts, then a second one 20 to 48 hours later. Other scenarios follow other rhythms: the table lists the timings documented as of October 2026, with their origin.
| Scenario | First email | Next emails | Source |
|---|---|---|---|
| Abandoned cart (e-commerce) | 2 to 4 h after checkout starts | Second email 20 to 48 h later | Klaviyo help center |
| Third cart email | Not applicable | Between 48 and 72 h, depending on the guides | Common practice in e-commerce guides, not documented by Klaviyo |
| Inactive customer (re-engagement) | Around 90 days without an open | Depends on your purchase cycle | Common threshold, covered in our article on relationship marketing |
One detail in the Klaviyo help center changes the setup. If your store syncs its events once an hour, a delay of 30 minutes will not hold. Klaviyo recommends at least 1 h 15 in that case. An email planned at 30 minutes can therefore leave an hour later.
The first message reminds the shopper what is in the cart. The second offers proof or answers an objection about shipping or returns. Keep a discount for a later message: offered up front, it teaches customers to abandon carts to get one. The article on triggering abandoned cart emails details the 3 data points required before the first send.
What does a follow-up earn?
The Klaviyo report published on October 2, 2026 draws on more than 110,000 customers. In it, the abandoned cart email earns the highest revenue per recipient of any flow: 6.77 dollars on average and 13.70 dollars for the top 10% of brands. The average click rate reaches 6%, against 11.3% for that top tenth. A flow’s ROI is its attributed revenue minus tool and sending costs, divided by those costs.
These figures come from stores running Klaviyo. The conversion rate of your own flow varies with your average order value and the quality of your sending list.
Who to follow up with, and with what message
Segmentation separates 3 situations. Identified visitors who have not bought get a reminder of the cart or the product page they viewed. Recent customers get an offer tied to their last purchase, with no promotion on the item they just paid for. Inactive customers enter a re-engagement scenario with a simple question or a useful piece of content.
The marketing automation tools of ESPs (email service providers) such as Klaviyo, Brevo or ActiveCampaign run these scenarios as flows. Each flow has a trigger tied to a CRM event, an exit condition (the purchase) and steps spaced by delays. These triggered emails form a follow-up sequence. Without an exit condition, a customer who bought in the meantime still receives the next step.
Email personalization relies on these events more than on the first name.
Why the open rate no longer proves anyone read the email
Apple Mail Privacy Protection, introduced with iOS 15 and macOS 12, preloads the images of every message. The tracking pixel is downloaded whether or not the recipient opens the email. According to Twilio SendGrid’s documentation, the sender can no longer tell a real open from a preload, and repeat opens are not reported either. Every protected address therefore shows up as “opened”.
Gmail behaves similarly. Since Google’s announcement of December 12, 2013, it serves all images through Google’s own proxy servers instead of the original host servers. The Apple side of it is still documented by Twilio.
Drive your flows on clicks or purchases instead. A condition such as “email 1 not opened, send email 2” wrongly removes protected Apple Mail readers from the follow-up, since their message looks opened by default. The open rate keeps some value as a trend on a large base. It does not qualify any individual contact.
Why verify the captured address before following up
The address typed into a pop-up or a checkout is the most fragile piece of data in the chain. A typo in the domain (gmial.com), a disposable address created to get past the step or a catch-all domain that accepts everything on arrival all lead to the same result: an email sent into the void. The bounce comes back as an NDR carrying code 5.1.1 (unknown address, format defined by RFC 3463).
Each nonexistent address produces a hard bounce that weighs on sender reputation. A follow-up flow runs continuously, and nobody inspects each send. Even a modest share of invalid addresses repeats at every cycle. Deliverability then drops across all campaigns, newsletters included.
Email address verification screens out these cases before the first send. It checks the address syntax, then queries the domain and the mail server (MX records). It plugs into the signup form through an API or runs in bulk on your existing database. A catch-all domain remains a special case: verification flags it as “risky” without guaranteeing the mailbox. Before your next campaign, run a sample of addresses from your cart flow through a verification and compare the hard bounce rate before and after.
On the authentication side, also check SPF, DKIM and DMARC on the sending domain.
What GDPR and the CNIL say about these follow-ups
The CNIL, France’s data protection authority, sets prior consent as the general rule for email prospecting of individuals. It requires a positive act: a dedicated checkbox, not pre-ticked. Accepting the terms and conditions is not enough.
One exception covers a customer who has already bought similar products or services from the same company. An account created without a purchase does not fall under it. Each email must identify the sender and offer a simple way to unsubscribe. The details are on the CNIL page on prospecting by email.
The article on GDPR in email marketing lists the consent evidence to keep. The legal rules for emailing complete the picture.
Frequently asked questions
Can you follow up with a visitor who has no email address?
No. Without a typed address, the site only holds an anonymous identifier. Only remarketing ads can target it.
How many follow-up emails for an abandoned cart?
Klaviyo documents two emails: the first 2-4 hours after checkout starts, the second 20-48 hours after the first. A third email at 48-72 hours is common practice in e-commerce guides.
Should you measure follow-ups with the open rate?
No, Apple and Gmail distort that measure. Use the click rate and attributed orders.
