SMS Marketing Through Klaviyo: When It Works, When It Doesn't, and How to Start

Every Shopify brand we work with eventually asks the same question: "Should we be doing SMS?"

The answer is almost always yes — but with a critical caveat. SMS is not email. The rules are different, the tolerance is lower, and the cost of getting it wrong is higher. Send too many messages and customers don't just unsubscribe — they block you. And unlike email, there's no "spam folder" middle ground. It either lands or it doesn't.

Here's the framework for SMS marketing through Klaviyo that actually works, based on what we've seen across multiple Shopify accounts.

Why SMS Works (When Done Right)

The numbers are compelling. SMS open rates sit around 90-95%. Not because people love marketing texts, but because text messages are inherently high-priority in how people use their phones. An unread text creates friction that an unread email doesn't.

Conversion rates reflect this. SMS campaigns to engaged subscribers consistently outperform email on a per-message basis. The catch is that you can send far fewer of them.

The real power of SMS isn't as a standalone channel. It's as an amplifier for your email program. SMS reaches people who might miss an email. It creates urgency that email can't match. And it's particularly effective for time-sensitive moments: flash sales, back-in-stock alerts, and the final hours of a promotion.

For one of our DTC clients, SMS contributed a small but meaningful portion of Klaviyo revenue. The channel was underutilized — we were conservative with it — and in hindsight, deploying it earlier and more strategically for high-intent moments would have driven significantly more revenue.

The 4-6 Rule: Frequency That Doesn't Burn Your List

Here's the most important rule: never send more than 4-6 SMS messages per month outside of major sale events.

That's it. Four to six. Not per week. Per month.

Email subscribers tolerate 2-5 sends per week because email is a lower-intrusion channel. SMS lives on the same screen as messages from friends and family. Every marketing text you send competes directly with personal communication.

Send too many and three things happen: opt-out rates spike, your compliance costs increase (every opt-out and message costs money), and the channel loses its power. SMS works because it's rare and urgent. Make it frequent and generic, and you've just created expensive email.

Where SMS Fits in Your Flow Architecture

SMS isn't a replacement for any email flow. It's an addition to specific high-intent moments within your existing flows.

Abandoned Checkout (High Impact)

This is the highest-ROI use of SMS in your flow architecture. Someone started checkout, entered their phone number, and left. They were moments away from purchasing.

Add an SMS touchpoint 1 hour after the checkout abandonment trigger — before your first email. Keep it short: the product name, a direct link to their cart, and urgency. Something like: "You left something behind — your [Product] is still in your cart. Complete your order: [link]"

Why SMS first? Because speed matters for abandoned carts. The longer someone is away from checkout, the less likely they return. SMS reaches them faster than email.

Back-in-Stock Notifications (High Impact)

When a customer requested a back-in-stock alert, they explicitly asked to be notified. SMS is the perfect channel for this because it conveys urgency about limited inventory that email can't match.

Send the SMS the moment the product is restocked. Follow with an email 30 minutes later for anyone who didn't click the SMS.

VIP Early Access (Medium-High Impact)

Your VIP customers opted into SMS because they want exclusivity. Deliver on that promise. Give them early access to new products and sales via SMS 2-4 hours before the email goes out.

This creates a genuine reason for customers to stay on your SMS list. If the SMS content is the same as email, delivered at the same time, there's no value in being subscribed to both.

Flash Sales and Urgency Campaigns (Medium Impact)

SMS is ideal for time-limited offers. "24-hour flash sale" or "Last 3 hours" messages drive immediate action. But use this sparingly — if every SMS is a flash sale, none of them feel urgent.

Reserve SMS flash sale messages for genuinely limited offers, maximum once per month.

The SMS Welcome Series: Keep It Short

When a subscriber opts in to SMS, send a brief welcome series. Not 5 messages. Not even 3.

Message 1 (Immediate): Confirmation of opt-in + the promised incentive (if they signed up for a discount). Include your brand name so they know who's texting.

Message 2 (Day 3-5): One value-driven message. Best-selling product, quick tip, or exclusive offer. This sets the expectation for what your SMS content will look like.

That's the series. Two messages. Don't overthink it. The purpose is to deliver the promised value and set expectations. Everything after this should be triggered by behavior or sent as part of your monthly campaign cadence.

Compliance Is Non-Negotiable

SMS compliance is stricter than email compliance. The rules:

Explicit opt-in required. Unlike email where a pre-checked box might slide, SMS requires clear, affirmative consent. The subscriber must actively choose to receive texts.

Every message needs an opt-out. "Reply STOP to unsubscribe" must be in every SMS. No exceptions. Klaviyo handles this automatically, but verify it's showing correctly.

Quiet hours. Don't send SMS before 8 AM or after 9 PM in the recipient's local timezone. Klaviyo's smart sending handles this, but double-check the settings, especially for brands with international audiences.

TCPA compliance (US). If you're sending to US numbers, the Telephone Consumer Protection Act governs your SMS marketing. Violations carry fines of $500-$1,500 per message. This isn't a slap on the wrist — it's existential.

GDPR (EU). Same consent requirements as email, but enforcement is stricter. Document when and how each subscriber consented to SMS.

Measuring SMS Separately

SMS revenue should be tracked and reported separately from email. Here's why: SMS costs money per message (unlike email, which is essentially fixed-cost at scale). You need to know the ROI per message to justify the channel.

In Klaviyo, SMS revenue is attributed separately in the dashboard. Pull these numbers monthly:

• SMS revenue (total and per-message)
• SMS click-through rate
• SMS opt-out rate (watch for trends)
• SMS list growth
• Cost per message vs. revenue per message

The economics should be clear. If each SMS costs $0.01-0.02 to send and generates $0.10+ in revenue on average, the channel is working. If the ratio gets tight, re-evaluate your targeting and frequency.

What Most Brands Get Wrong

The biggest SMS mistake isn't sending too many messages or writing bad copy. It's treating SMS like a smaller version of email.

Email is a content channel. You can tell stories, show product galleries, include multiple CTAs. SMS is a notification channel. One message. One action. One link.

Every SMS should be 1-3 sentences. Include the brand name, the key message, a link, and the opt-out. That's it. No paragraphs. No multiple offers. No "P.S." lines.

The second biggest mistake is not tracking it separately. If you can't show the client exactly how much revenue SMS generated versus how much it cost, you can't justify the channel or optimize it.

The Bottom Line

SMS is a high-impact, low-frequency channel that amplifies your email program. It's not a replacement for email strategy. It's the sharp point that cuts through when timing and urgency matter most.

Build it into your abandoned checkout flow first. Add back-in-stock and VIP early access. Keep your monthly campaign SMS to 4-6 messages. Track everything separately.

Done right, SMS becomes the most efficient revenue channel per touchpoint in your entire Klaviyo setup.