Email + SMS Marketing in Klaviyo: How to Run Both Without Annoying Your Customers

The brands that treat SMS as a secondary email channel (just firing texts whenever they send a campaign) are the ones with 15% opt-out rates and dismal list retention. SMS works when it’s treated as a fundamentally different medium with its own rules, cadence, and content hierarchy. Run it alongside email correctly and you’ll see 20–30% revenue lift on the flows where it matters most. Run it wrong and you’ll spend six months rebuilding a burned list.

One number that frames the whole conversation: 75.4% of consumers prefer to hear from brands via email, compared to 19.2% who prefer SMS and 15.8% who prefer social media. That doesn’t make SMS irrelevant. It makes it complementary. Email is where the relationship lives. SMS is where the urgency hits. Email also averages $36 in revenue for every $1 spent, and automated email flows alone drive a 33.48% click-to-conversion rate versus 5.88% for standard campaigns. The play isn’t SMS vs. email. It’s using each channel for what it does best.

Here’s how to build a dual-channel program in Klaviyo that customers don’t hate.

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The Channel Hierarchy: What Goes Where

Email and SMS have different strengths, and the mistake is treating them as interchangeable. Think of it as a message hierarchy:

Email is best for:

• Long-form content (educational, story-driven, product launches with context)
• Visual content (lookbooks, product photography, multi-section campaigns)
• Campaigns where timing flexibility is acceptable (newsletters, non-time-sensitive promotions)
• Any communication requiring explanation or nuance
• Re-engagement: you can send email to cold subscribers with less damage than SMS to a cold number

SMS is best for:

• Time-critical alerts (sale goes live in 2 hours, limited stock, flash offers)
• Short, action-oriented messages with a single link
• High-urgency abandoned cart follow-ups
• BFCM day-of announcements
• Back-in-stock notifications where speed matters

The test before you send a text: Would this message feel urgent and useful if it arrived at 10am on a Tuesday? If the answer is no, it’s an email. SMS has the attention profile of a phone call from a friend. It gets opened within 3 minutes on average. Wasting that attention on non-urgent content is how you train your subscribers to opt out.

75% of US emails are opened on smartphones, which creates a natural bridge between the two channels. Your subscribers aren’t switching between “email mode” and “text mode.” They’re on the same device. Timing and spacing between email and SMS touches matters more than most brands realise, because both compete for attention in the same notification feed.

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Frequency Rules: How Often to SMS Without Burning Your List

Most brands that burn their SMS lists don’t know they’re doing it until the opt-out rate spikes. The damage is incremental: an extra text here, an extra text there, until subscribers start opting out faster than you’re adding new ones.

Campaign SMS: Maximum 4–6 per month for most ecommerce brands. More than that requires either genuine urgency every time (rare) or a product drop cadence that justifies frequent contact. For reference, BFCM will likely use 3–4 of your November texts on its own, so plan accordingly.

Transactional SMS: Shipping confirmations, order confirmations, delivery alerts. These are expected and welcome at any frequency. Customers opted in to transactional messages implicitly when they bought. These do not count against your marketing SMS budget.

Flow SMS: Embedded within automated flows, SMS touches should be spaced by at least 48–72 hours from any previous message (email or SMS) in the same flow. This prevents the sensation of being bombarded during a cart abandonment or post-purchase sequence.

The 24-hour rule for BFCM: During Black Friday weekend, you have permission to text daily, but only if every message has a genuinely different and time-sensitive offer. “Last chance” has to be last chance.

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SMS Compliance Basics

Klaviyo’s SMS is built for the US market under TCPA (Telephone Consumer Protection Act) compliance requirements. Getting this wrong isn’t just a deliverability problem. It’s a legal one.

TCPA essentials:

• Express written consent is required before sending any marketing SMS. A customer giving you their phone number at checkout for order updates is NOT consent for marketing texts. These are separate opt-ins.
• Opt-in must be specific to SMS marketing. Your opt-in language must state they’re agreeing to receive recurring automated marketing text messages. Klaviyo’s built-in form templates have compliant language. Use them.
• Must include your brand name in every SMS message (Klaviyo handles this automatically if configured correctly)
• Must include an opt-out mechanism in every message: “Reply STOP to unsubscribe” (again, Klaviyo handles this natively)
• Honour opt-outs immediately. TCPA requires removal within 10 business days; Klaviyo processes them in real time.

A note on Australian and UK compliance: If you’re sending to non-US numbers, different laws apply (Australia’s Spam Act 2003, UK’s PECR). Klaviyo’s compliance framework is primarily built around TCPA. If you’re in the AU or UK market, consult a local compliance resource before activating SMS.

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Klaviyo SMS Setup: Key Decisions

Dedicated long code vs. short code vs. toll-free number:

• Long code (10DLC): A standard 10-digit number registered to your brand under the A2P 10DLC campaign registry. Best for mid-volume senders (under ~100,000 messages/month). Lower throughput (1 message per second) but dedicated to your brand.
• Toll-free number: Quicker to set up, no 10DLC registration required, but toll-free verification is still required. Good for starting out. Shared throughput considerations.
• Short code (5–6 digit): Highest deliverability and throughput (100 messages/second). Required for high-volume BFCM sends at scale. Setup takes 8–12 weeks and costs significantly more. Not necessary until you’re sending 500,000+ SMS/month.

For most Shopify + Klaviyo brands under $10M revenue, a verified 10DLC long code is the right starting point. Set it up well before BFCM. Carrier registration can take 2–4 weeks.

SMS credits in Klaviyo: Klaviyo bills SMS on a per-message credit basis. Standard SMS (160 characters or fewer) uses 1 credit per recipient. Messages over 160 characters are segmented by carriers into multiple messages, each consuming a credit. Write your SMS copy to stay under 160 characters including your brand name prefix and STOP language. Use a character counter. Every extra character above 160 doubles your cost.

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Flow Integration: SMS as a Parallel Channel

The highest-value use of SMS in Klaviyo is within flows, where you can sequence email and SMS touches with precise timing rather than firing them simultaneously.

The wrong way: Send the abandoned cart email AND the abandoned cart SMS at the same moment. This is disruptive and wastes the unique channel properties of each medium.

The right way: Stagger by channel strength. Email is the primary touch; SMS is the urgency escalator.

Example abandoned cart sequence:

• T+1 hour: Email 1: reminder, no discount
• T+24 hours: Email 2: social proof, light incentive
• T+48 hours: SMS: “Still thinking it over? Your cart expires tonight. [link]”
• T+72 hours: Email 3: last chance with discount code

The SMS at 48 hours works because it arrives through a different channel with a different urgency signal. It doesn’t feel redundant. It feels like a separate, time-sensitive prompt.

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The 3 Flows That Benefit Most From SMS Integration

1. Abandoned Cart SMS lifts cart recovery rate by 5–10 percentage points when added to an email-only flow. The key is adding the SMS touch at the 48–72 hour mark, not within the first 6 hours (where email alone typically handles it effectively and SMS feels aggressive). Use SMS to surface the urgency of cart expiry or limited stock.

2. BFCM Launch The biggest SMS revenue opportunity of the year. An SMS sent at 6am on Black Friday with “Our biggest sale is LIVE. 30% off everything. Shop now: [link]” will generate clicks within 3 minutes of send, front-loading your BFCM traffic before the inbox gets noisy. This alone can shift 15–25% of your BFCM revenue to the first 2 hours of the sale window.

3. Win-Back SMS win-back outperforms email win-back for one simple reason: a subscriber who’s stopped opening emails still has a functioning phone number. An SMS win-back sequence (1–2 texts, high-value offer, clear opt-out path) can reactivate 8–15% of subscribers who have completely ghosted your email program. It is a genuinely different channel accessing a different behaviour pattern.

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Measuring SMS Performance in Klaviyo

Klaviyo tracks SMS analytics at the flow and campaign level. The metrics to monitor:

Click rate: SMS click rates of 15–25% are achievable with well-timed, relevant messages. Below 10% suggests the content or timing is off. Above 25% indicates exceptional relevance. Note what worked.

Opt-out rate: Industry standard is under 3% per campaign. Anything above 5% is a signal: either frequency is too high, the content isn’t relevant, or your acquisition method isn’t setting the right expectations. BFCM sends will typically see elevated opt-outs (3–6%), so budget for this.

Revenue per send: SMS revenue per send should exceed email revenue per send for the flows where you’re using it, because SMS is reserved for your highest-intent moments. If your SMS abandoned cart touch isn’t generating at least $0.30–$0.50 RPR, the timing or offer needs revision.

Cost per SMS send: Calculate your SMS channel ROAS as (SMS-attributed revenue) / (SMS credit cost). A healthy ratio is 15:1 or above. Below 10:1, the channel is working but thin. Below 5:1, reassess whether the channel is ready to scale.

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The Bottom Line on Dual-Channel

Email and SMS are not the same channel with different formatting. They have different costs, different compliance requirements, different timing windows, and different audience expectations. Running both well means:

• Keeping SMS reserved for genuinely time-sensitive, high-urgency moments
• Staggering touches within flows rather than sending simultaneously
• Staying under 160 characters to control credit costs
• Monitoring opt-out rates weekly and adjusting frequency before they spike
• Ensuring carrier registration is completed well before your highest-send periods

Brands that treat SMS with this discipline consistently see 20–30% incremental revenue lift over email-only programs, with opt-out rates that stay sustainable long term.

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Sources

• Email Vendor Selection, Email Marketing Statistics
• Litmus, The ROI of Email Marketing