Your subject line is the only part of your email that everyone sees. Everything else — the design, the copy, the offer — depends on the subject line doing its job first. For Shopify brands, where email competes with dozens of other DTC newsletters in the same inbox, a strong subject line is not a nice-to-have. It is the difference between a 20% open rate and a 40% open rate, which on a 10,000-person list is 2,000 additional people seeing your campaign.
What Makes a Subject Line Work
Good subject lines do one or more of three things: they create curiosity, they state a clear benefit, or they create a sense of urgency. The worst subject lines try to do all three at once and end up doing none of them well. Pick one angle per email and commit to it.
The other non-negotiable: the subject line must match what is in the email. If the subject line promises something the email does not deliver, your open rates go up once and your unsubscribe rates go up permanently.
Subject Line Formulas That Consistently Work
The Direct Offer
When you have a real offer, say what it is. Vague subject lines about "something exciting" underperform direct offers every time.
- "20% off — this weekend only"
- "Free shipping ends tonight"
- "Buy two, get one free — starts now"
The Curiosity Hook
A question or an incomplete thought that can only be resolved by opening the email. The key is that the payoff must justify the setup — if the email does not answer the question in a satisfying way, it damages trust.
- "You are probably making this mistake with your skincare routine"
- "We almost did not release this one"
- "The email we were nervous to send"
The Social Proof Lead
Numbers and real reactions are persuasive in subject lines, especially for products where peer validation matters.
- "5,000 people can not stop repurchasing this"
- "Our most returned-to product in 2025"
- "Why this sold out in 48 hours"
The Personal Address
First-name personalisation has declined in effectiveness as it became universal, but subject lines that feel personal without using the name still outperform generic ones. Think about what you would write to one customer you knew well.
- "We thought of you when we made this"
- "A quick note before the sale ends"
- "This is the last email about [product launch]"
The Announcement
When you have something genuinely new, lead with it directly. Novelty is a strong open driver — but only if the product or news is actually new.
- "Introducing [Product Name]"
- "It is finally here: [collection name]"
- "New: [Product]. Available now."
Subject Line Length
Most email clients display between 35 and 60 characters in the inbox preview. On mobile, it is often closer to 30–40. Write your subject line to make sense within the first 40 characters, even if the full line runs longer. Front-load the most important word or number — do not bury the offer at the end of a long sentence.
Preview Text: The Subject Line's Partner
The preview text (also called preheader) appears directly after the subject line in most email clients. Treat it as a second subject line, not an afterthought. If the subject line is the hook, the preview text is the set — it should extend the thought or add context that increases the chances of an open.
- Subject: "We almost did not release this one" → Preview: "Three years in development. Worth the wait."
- Subject: "20% off — this weekend only" → Preview: "Use code WEEKEND at checkout. Ends Sunday."
- Subject: "Introducing [Product Name]" → Preview: "Everything we could not fit in the campaign video."
What to Avoid
- Spam trigger words in all caps: FREE, URGENT, ACT NOW, CLICK HERE. These reduce deliverability before anyone even sees the subject line.
- Excessive punctuation: "You're going to LOVE this!!!" is a fast path to the promotions tab.
- Clickbait that does not pay off: If the subject line creates curiosity, the email must satisfy it.
- The same format every time: If every subject line is a discount announcement, your subscribers start treating your emails as coupons and stop reading the ones that are not. Vary your approach.
Testing Subject Lines
The only way to know what works for your specific list is to test. A/B test one variable at a time — subject line format, length, whether you use a number, first-person vs second-person — across sends of at least 500 people per variant to get statistically meaningful results. Klaviyo and Omnisend both support A/B subject line testing with automatic winner selection.
If you want to increase overall email performance — not just open rates — subject lines are the right place to start, but increasing Shopify email open rates involves several other levers alongside subject line optimisation.