SMS marketing: a different medium with stricter rules
SMS is not a shorter email. Consent requirements are stricter, the delivery path is governed by carriers rather than mailbox providers, and the cost of getting it wrong is regulatory rather than reputational. This page covers consent, sender registration, timing, and where SMS genuinely outperforms email.
- Consent
- Explicit opt-in
- Quiet hours
- Respected
- Segments
- Purchasers
- Length
- Single segment
How is SMS marketing different from email?
SMS reaches a device someone carries and usually reads within minutes, which makes it powerful and intrusive in the same measure. That combination is why the rules around it are tighter: there is no spam folder to absorb a mistake, and no equivalent of ignoring a message you did not want.
Three structural differences drive everything else. Consent for SMS must generally be explicit and separately obtained — email consent does not carry over. Delivery is governed by carriers who enforce registration and content rules directly. And each message costs money to send, so volume has a floor price that email does not.
The practical consequence is that SMS rewards restraint. A list that receives two well-chosen messages a month will outperform one receiving eight, because the opt-out rate on the second list compounds until there is no list left.
What consent does SMS marketing require?
SMS marketing requires express consent obtained specifically for SMS, and in most jurisdictions that consent must be separate from any other agreement. A checkbox that bundles SMS with terms of service is not valid consent in the places that matter most.
The specific requirements vary by jurisdiction, and the safest design satisfies the strictest one you are subject to. Broadly, this means: the person actively opted in, the opt-in explicitly mentioned marketing messages, they were told roughly how often and that rates may apply, and you retained a record of exactly what they agreed to and when.
Retaining the consent record matters as much as obtaining it. In a dispute the question is not whether someone consented but whether you can demonstrate it — which means storing the wording shown, the timestamp, and the source, not merely a boolean.
- Express written consent
- An affirmative action specifically agreeing to marketing SMS. Cannot be bundled with other terms or pre-ticked.
- Double opt-in
- The subscriber confirms by replying or clicking. Not required everywhere, but it produces the cleanest evidence and the most engaged list.
- STOP handling
- Replying STOP must unsubscribe immediately and automatically. This is a carrier-level requirement, not a courtesy.
- Quiet hours
- Windows during which marketing messages must not be sent, based on the recipient's local time rather than yours.
- Sender registration
- Carriers require registration of the sending brand and campaign before delivering application-to-person traffic. Unregistered traffic is filtered or blocked.
- Consent record
- The stored evidence: what wording was shown, when, from which page or channel. The artifact that makes consent provable rather than asserted.
Why do SMS messages fail to deliver?
SMS delivery failures usually come from carrier filtering rather than a wrong number, and the most common cause is unregistered or misregistered sending. Carriers require brands and campaigns to be registered before they will carry application-to-person traffic, and unregistered traffic is filtered silently.
Content triggers filtering too. Public link shorteners are heavily filtered because they obscure the destination, so a branded or platform-provided short domain is materially safer. Certain regulated categories face additional restrictions regardless of registration status.
Message length also matters more than it appears. A single SMS segment is 160 GSM-7 characters, but a single emoji or curly quote switches the whole message to UCS-2 encoding, dropping the segment to 70 characters. A message that looks like one SMS can silently become three, tripling its cost.
When is SMS the right channel?
SMS is right when the message is time-critical, short, and expected. A delivery window, an appointment reminder, a back-in-stock alert someone explicitly requested, a one-time passcode — each is useful precisely because it arrives immediately.
It is the wrong channel for anything requiring browsing, comparison, or consideration. A newsletter, a product roundup, or a detailed announcement all need room the medium does not have, and pushing them into SMS produces a link with no context — which is both ineffective and indistinguishable from a phishing message.
The useful test before sending: would this person be glad their phone buzzed for this? If the honest answer is no, it belongs in email.
How Moosewave approaches SMS
Moosewave treats SMS as a step inside the same automation flows as email rather than a separate system, so a lifecycle sequence can move between channels without two tools disagreeing about who has already been contacted.
SMS consent is tracked as its own permission, distinct from email consent, because they are legally distinct and combining them is the most common compliance failure in the channel.
- SMS as a step in the same flows as email, sharing one view of the subscriber
- SMS consent recorded separately from email consent, with the wording and timestamp retained
- Automatic STOP handling and global suppression across both channels
- Quiet-hours enforcement based on the recipient's local time
- Segment counting that shows encoding and cost before you send, not after
Moosewave is in private early access. Join the waitlist for an invitation.
Common questions
Can I send SMS to people who gave me their email address?
No. SMS consent must be obtained specifically for SMS in most jurisdictions, and having a phone number is not permission to message it. Even where the rules are looser, sending to someone who never asked produces opt-out and complaint rates that damage the channel quickly.
How many characters is one SMS?
160 characters using the GSM-7 alphabet. A single emoji, curly quote, or accented character switches the message to UCS-2 encoding and drops the limit to 70 characters, so a message that appears to be one SMS can silently become three — and be billed as three.
How often should I send marketing SMS?
Considerably less often than email — two to four times a month is a common ceiling, and many senders do well with less. The channel's advantage is that messages get read, and that advantage disappears the moment recipients start associating your name with interruption.
Do I need to register my brand to send SMS?
In most markets, yes, for application-to-person traffic. Carriers require brand and campaign registration before they will reliably deliver, and unregistered traffic is filtered or blocked without a delivery failure that is obvious from your side.
Related
Open rates stopped meaning what they used to. Which email metrics still carry signal, how attribution works, and how to read a campaign report honestly.
Forms, popups, and embeds that grow a list without poisoning it. How double opt-in, consent capture, and form placement affect both growth and deliverability.