SMS Marketing: Definition, Rules and What Actually Works

TL;DR. SMS marketing is sending commercial messages to consenting contacts. It is an urgency channel, not an acquisition channel and not a second promotional channel. Used that way : expiring carts, limited restocks, closing promotions, it adds incremental revenue. Used as one more newsletter, it empties a list within months, because an SMS list does not rebuild the way an email list does.

SMS suffers from a structural misunderstanding. Its surface metrics are spectacular: near-immediate reading, open rates far beyond email. The conclusion most brands draw is that they should send more.

That is precisely the decision that kills SMS programs.

What SMS marketing is

SMS marketing means sending commercial messages by text to people who have consented to that channel.

It differs from transactional SMS, which accompanies an action the customer initiated: order confirmation, verification code, dispatch notification. The two do not fall under the same regime, do not address the same contacts and are not steered the same way. Covered in transactional vs marketing SMS.

The boundary matters in practice: slipping a commercial offer into a delivery message reclassifies it and takes you outside the transactional framework.

The consent rules

For prospecting to individuals, the principle is prior consent. That consent must be:

• free, so not conditioned on access to the service;
• specific, so collected separately from terms acceptance;
• informed, so accompanied by the controller's identity and the purpose;
• unambiguous, so the result of a positive act : a pre-ticked box is not consent.

Every message must also carry a simple opt-out.

One confusion worth clearing: the French sending windows, before 8am, after 10pm, Sundays and public holidays, do not come from the law. Article L34-5 of the postal and electronic communications code sets none, and the CNIL guidance on electronic marketing does not mention any either. Mobile operators apply them at the delivery stage.

The practical effect is the same, but the reasoning differs: you can be fully compliant and still see messages undelivered. And repeatedly sending outside the window weighs on the routing of your other campaigns, which no statute penalises but your provider will observe.

The detail for France, where the CNIL guidance is the strictest we work under, is in SMS and GDPR in France. The general prospecting framework is in GDPR and email marketing.

The practical point that causes the most trouble: a list of numbers collected without traceable consent cannot be used. Neither buying it in good faith nor the age of the collection changes that.

Why SMS is not a shorter email

Three structural differences, which explain most steering errors.

Every send costs. Unlike email, whose marginal cost is near zero, every text is billed. A badly targeted campaign does not just cost attention, it costs money.

The list does not rebuild at the same rate. Acquiring a number costs more than acquiring an email address, consent is harder to obtain, and opting out feels final to the customer. An SMS list is managed like a depletable stock, not like a tap.

Intrusion is perceived differently. SMS arrives on a channel most people reserve for people they know. Tolerance for solicitation is markedly lower than in an inbox.

The four use cases that produce revenue

1. Checkout abandonment

The most profitable window in the whole program. The customer was seconds from ordering, intent is at its peak, and reading delay decides conversion.

Short message, one action, direct link to the restored cart.

2. Cart abandonment, above a threshold

Relaying the email flow, triggered at H+4, and only on carts above average order value. The threshold is what makes the flow profitable: on a €30 basket, the cost of the text eats the margin.

The full flow logic is in Klaviyo abandonment flows.

3. Back in stock

The case where SMS consistently outperforms email, for a simple reason: the contact explicitly asked to be told, and availability is time-limited. The message is expected.

4. The closing hours of a promotion

Once per event, not three times. SMS creates real urgency on a real deadline. Repeated, it becomes noise the reader learns to ignore.

What does not work

The SMS newsletter. Editorial content has no place on a channel where every message costs and space is constrained.

Duplicating the day's email. If the contact already received the offer by email that morning, the afternoon text adds nothing but irritation. The non-overlap rule is what makes a multichannel program viable : see Klaviyo omnichannel marketing.

Sending to the whole list. Segmentation matters more in SMS than in email, precisely because every send costs.

Weekly frequency. Two to four sends a month on a general-audience list. Beyond that, the 90-day cumulative opt-out rate breaks down and the list empties faster than it fills.

A message with no visible sender. On a channel with no subject line and no header, the brand has to be legible in the opening words. A text that starts with a promotion without saying who is writing reads as spam, and gets reported as such.

A bare link. An unbranded short URL, inside a message nothing identifies, ticks precisely the signals of a fraudulent text. The tracking subdomain should carry your brand.

Those last two carry a cost the others do not: in France an unsolicited text, or one perceived as such, can be reported to 33700, the platform dedicated to fraudulent and unwanted SMS. A report is not corrected the following week.

How to measure

Read rate is a poor steering metric: it stays high even on a fatigued list. Three useful ones:

Revenue per recipient, which correctly arbitrates volume against fatigue. It sits at the centre of our reference framework: below €0.10 per recipient, the list is being solicited without being monetised.

90-day cumulative opt-out rate, the early saturation signal.

Holdout incrementality, which separates revenue SMS creates from revenue email would have captured anyway.

The general framework is in lifecycle email marketing KPIs.

FAQ

Are there legal hours for sending marketing texts in France?

Not in statute. Article L34-5 of the postal and electronic communications code sets no time window, and the CNIL guidance on electronic marketing mentions none. The before-8am, after-10pm, Sunday and public-holiday windows are applied by mobile operators at the delivery stage, so the practical constraint holds even though its source is not the law.

What is SMS marketing?

Sending commercial messages by text to consenting contacts, distinct from transactional SMS.

Is SMS marketing legal?

Yes, subject to prior, free, specific and informed consent, with an opt-out in every message.

What read rate should we expect?

Very high, but it is a poor steering metric. Follow revenue per send.

What is the difference between marketing and transactional SMS?

Transactional accompanies a customer-initiated action and needs no marketing consent.

How much does SMS marketing cost?

Routing depends on volume and destination; the real cost is list attrition.

Going further

Technical implementation is in Klaviyo SMS setup and opt-in flows and Klaviyo SMS marketing.

To scope a programme, see our SMS marketing agency.

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