SMS marketing only works if your messages land in your subscribers' inboxes, and if every message you send respects the laws that protect their privacy. This guide walks through what you need to know to grow a compliant SMS list, send compliant messages, and keep your deliverability strong.
Disclaimer: this guide should not be relied on as legal advice. Klaviyo encourages you to work with your legal counsel to make sure your SMS programme is compliant with the laws that apply to it.
List growth compliance
SMS marketing is regulated to make sure people don't receive messages they haven't agreed to. In the US, this includes the TCPA (enforced by the FCC) and CAN-SPAM (enforced by the FTC). In Canada, it's the Canadian Anti-Spam Legislation (CASL). In the EU, it's the General Data Protection Regulation (GDPR), and in the UK it's the UK GDPR and the Privacy and Electronic Communications Regulations 2003 (PECR). In Australia, it's the Spam Act 2003 and the Spam Regulations 2021. Falling foul of these rules can mean significant fines and legal action, so it's essential to grow your list and message your subscribers in a way that's compliant with the laws, industry guidelines, and carrier requirements that apply to you.
Before you can text someone, you need their express written consent. In the US, that means your SMS sign-up forms need to clearly state:
- That messages will be marketing or promotional in nature
- That messages may be sent via an autodialer
- That agreeing to subscribe isn't a condition of any purchase
- Your message frequency (e.g., "message frequency varies")
- That message and data rates may apply
- A link to your brand's mobile terms and conditions and privacy policy
- Opt-out and help instructions
Klaviyo's SMS sign-up forms include this language by default, so you don't have to remember to add it yourself, though you can adapt it with your legal team's help. Requirements vary by country, so check what's needed for Canada, the UK, and Australia before you message customers in those regions.
In the UK and Australia, branded sender IDs only let you send one-way, so customers can't text you back. And list growth compliance doesn't stop at new sign-ups: if you're importing existing SMS contacts into Klaviyo, you'll be prompted to upload the date each subscriber gave consent, alongside their phone number, so your records stay complete from day one.
Beyond your website, there are plenty of compliant ways to grow your list: embed a sign-up form in your footer or order confirmation page, use a pop-up for new visitors, invite people through features like Instagram's link stickers, capture sign-ups on product pages and follow up with relevant questions by text, or email a segment of subscribers who haven't yet opted in to SMS with a clear call to action.
Message compliance
The information you need to include in your messages differs by country, so review the requirements for Canada, the UK, and Australia before sending to customers in those regions. Two of the most common compliance mistakes are texting people who've never subscribed or who've unsubscribed, and continuing to message a number that's been reassigned after someone cancels their contract or switches carriers. Klaviyo checks each subscriber's consent before every send, and automatically removes SMS consent when a number is deactivated or ported to a new carrier.
Include your brand name in every message
Text is a far more intimate channel than email, so your customers want to know who's texting them. Klaviyo automatically adds your brand name to every SMS and MMS message, and it's a legal requirement in the UK, the EU, and Australia. (MMS itself isn't currently available in the UK or Australia, due to carrier limits and the use of branded sender IDs.)
Respect quiet hours
Regulations mean you can only send messages between 9am and 9pm in the recipient's local time zone, and some US states set stricter limits still. Klaviyo's SMS Quiet Hours safeguard applies automatically to your campaigns and flows, so messages triggered outside business hours wait until it's appropriate to send.
Make opting out easy
In the US, Klaviyo recommends including opt-out language in every message, with opt-out instructions at least once a month; some carriers, like T-Mobile, ask for explicit instructions every fifth message. In Canada, the UK, the EU, and Australia, include opt-out language or a link in every message (a link is required in the UK when using branded sender IDs). If you hold a Canadian short code, you're also required to recognise French opt-out keywords, which Klaviyo supports by default. Klaviyo automatically adds the relevant opt-out language or link to every message you send.
Two-way conversations
SMS Conversations lets you reply to subscribers in real time, but only once they've opted in to your SMS list specifically, not just email, so you can't accidentally breach two-way messaging rules. This feature isn't currently available in the UK or Australia.
SMS deliverability essentials
Deliverability is the percentage of your messages that actually reach a subscriber's device. You're billed for every message you send, not just the ones that arrive, so it pays to partner with a platform that reports transparently on what's sent, delivered, and clicked, and tells you why any message failed.
Carriers filter messages containing SHAFT terms (sex, hate, alcohol, firearms, and tobacco), as well as related trigger words, even if your business has nothing to do with those industries. It's worth reviewing your message copy against a list of common spam trigger words before you send.
Choosing the right phone number
Toll-free numbers are free, quick to set up, and available in the US and Canada; Klaviyo can scale their throughput from 3 to 25 messages a second as your list grows.
Dedicated short codes cost more and take longer to lease (typically 8 to 12 weeks), but carriers trust them more, so they suit brands sending to over 100,000 people a month. Short codes are available in the US and Canada, though you'll need a separate one for each country.
Long codes can receive inbound messages, which unlocks features like double opt-in, click-to-text, subscribe keywords, and two-way conversations. They're only available in the UK and Australia, aren't branded, and only work for sending within the one country they're registered to.
Branded sender IDs display your brand name as the sender for one-way messages. They're only available in the UK and Australia, and Klaviyo includes one free of charge.
Avoid shared short codes: if another brand using the same code sends non-compliant messages, everyone sharing it can see their deliverability suffer. Mobile carriers have moved to ban shared short codes altogether, and Klaviyo has never supported them.
Verified numbers and throughput
A verified number helps aggregators, the companies that sit between your SMS platform and carrier networks, recognise your brand and keep your messages out of spam filters. Klaviyo verifies your toll-free number for you and adjusts your throughput automatically as your list grows, so new subscribers aren't left waiting. Regulated industries, such as firearms and cannabis, can't register a number for legal reasons set by carriers at a federal level.
Why a unified platform matters
Compliance and deliverability work best when they're built into your SMS platform from the start, rather than bolted on afterwards. Because Klaviyo combines email and SMS in one place, and draws on established SMS partnerships like Twilio, you get a single view of consent, performance, and engagement across both channels, so you can focus on building relationships instead of worrying about the mechanics of sending.
Power smarter digital relationships with Klaviyo
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