Email subject lines for ecommerce: what actually gets opened

Ecommerce email subject lines and open rate patterns for ecommerce stores in 2026

We ran a test last year with a client. Same audience, same offer, same email inside. Two subject lines. One of them said "20% off everything this weekend." The other one said "We're doing something we haven't done before." Vague. No offer revealed. No discount amount.

The vague one got a 38% open rate. The transparent one got 19%.

We assumed it would go the other way. It didn't.

Since then I've stopped trying to argue for transparency in the subject line. The tests keep saying the same thing.

Why showing the offer hurts you

When you write "20% off everything this weekend" in the subject line, you've given the subscriber a complete summary of the email. They can make a decision about whether to shop right now without ever opening it. If they're not in shopping mode at that moment, they scroll past. You handed them the exit.

The vague version leaves a gap. Something unresolved. People open emails to close gaps. The offer lands better once they're already inside anyway.

The mystery discount version of this is the clearest proof. Instead of "here's 15% off" in the subject line, you tell them there's an exclusive offer waiting inside. "Your discount is in here." "Open this one." Sounds like it'd annoy people. It doesn't. It converts better than showing the number, pretty consistently, because people are more motivated by not knowing something than by knowing a discount they haven't yet decided they care about.

The personalization token thing is the same mistake dressed up. "[First name], don't miss this" technically has your name in it, but everyone knows that came from a database field. It doesn't feel personal. What actually drives clicks is a subject line that reads like someone wrote it mid-week because they thought of something worth sharing. "I'm a little obsessed with this new collection." "Had to share this." "Quick thing before the weekend." Just sounds like a person. The click difference compared to merge-tag versions is real, and consistent across the boards we've seen.

The subject line length

Mobile email inbox showing subject lines cut off on a phone screen

Between 78% and 90% of email opens happen on a phone. On a phone, the subject line gets cut off somewhere around 38 characters. Same with preview text. So if you're writing 70-character subject lines, most of your list only sees half of it.

Stores with consistently good open rates tend to write around 2 to 5 words in the subject line, one sentence for preview text, combined under 55 characters. Not because some study said those numbers. That's just what fits on the screen your subscribers are actually reading on.

Shorter subject lines read different too. "They're finally here." "You might want this." "Still thinking about it?" Sounds like a text, not a campaign. With inboxes full of AI-generated marketing right now, the human-looking ones get opened and the blast-looking ones get skipped, or at some point unsubscribed.

Subject line and preview text are one move, not two separate decisions. Open a loop in the subject. Extend it with the preview without closing it. "They're Finally Here" followed by "If you want the cold hard facts, we got them..." Neither does much alone. Together there's something unresolved, so you open it.

What I see constantly is preview text that just says the subject line again. "20% off this weekend" followed by "Save 20% on all products this weekend." Same thing twice. Nothing unresolved, no tension. And you've confirmed to the subscriber that this is a promotional email they can skip.

A few patterns worth stealing

A/B test showing two subject line variants with different open rates

Subject lines that look like direct messages outperform announcement-style ones by a lot. "Everything okay?" "Hey, quick thought." "Need some help?" I know, these seem like they'd irritate people. They don't. They get opened because they don't look like campaigns. Save them though — they wear out fast if you use them every send.

Teasers with specific detail work for a different reason. "That jacket you were looking at." "Your cart has been patient." Even going to a broad list, these read like they're for one person. The impression of relevance does the job even when there's no actual personalization behind it. I personally find this a little unsettling every time I think about it for more than thirty seconds, but the data is the data.

The real deadline subject line is the most consistent performer I've seen. "Last chance, this closes tonight" — when it's actually closing that night, it converts. The problem is everyone uses urgency language even when nothing's ending, and subscribers figure it out eventually. The trust depletes slowly. Takes a long time to come back.

The sender name is probably the most overlooked test in ecommerce email. "Jake from Fieldwork" versus "Fieldwork." Most stores have never tried it. Subject lines get read differently depending on who sent them. People respond better to people than to brands, and that gap has been getting wider. Worth running this before you spend weeks on subject line copy, honestly.

On spam: all caps in the subject line filters fast and reads badly. A stack of high-frequency spam words will trigger filters even when each word alone is fine. Two or three emoji is normal. Six looks like a late-night TV ad.

And behind all of it is sender reputation. Filters look at how your recent sends performed. Good open rates compound into better inbox placement. Bad subject lines affect where next month's campaigns land.

The real effort

None of these patterns last forever. What's working right now started fading for early adopters back in 2024. The stores I've seen consistently hit 40%+ open rates aren't following a list — they run two variants on every send, look at what their own list responds to, and adjust.

Two variants, same campaign, split down the middle. One real test teaches you more than a month of reading about best practices. And it compounds because you're building a picture of your specific subscribers, not some study average.

Most stores don't test because there's no time. Having two subject line ideas requires not being rushed. And most small store owners are fitting email marketing strategy and campaign planning into a Tuesday afternoon between shipping orders and a supplier call. The testing just doesn't happen.

MailCommerce AI generates subject lines and preview text as part of the full email creation process, matched to the campaign content and your brand voice. You paste your store URL, it reads your products and brand, and builds complete emails with subject lines included, ready to push to Klaviyo, Mailchimp, Omnisend, or whatever ESP you're using. You can generate the variants needed for your testing in a matter of minutes.

Free to try, no credit card required. Start here.