SMS content restrictions depend on the traffic type and the country: OTP routes often accept only verification codes, transactional routes forbid marketing, and promotional traffic needs consent, opt-out and allowed hours. Some categories, such as gambling, loans, adult content, alcohol, tobacco and cannabis, are restricted, or blocked by carrier filtering, on many routes regardless of type.
Why content matters to routes
Operators protect their subscribers with SMS firewalls that scan sender IDs, links and keywords. A route is approved for a specific use, and traffic that does not match it can be blocked, can lead to fines for the supplier, or can get the whole connection suspended. That is why suppliers ask for sample messages before they open a route. Filtering is explained in SMS firewalls explained.
Restrictions by traffic type
| Traffic type | Usually allowed | Usually not allowed |
|---|---|---|
| OTP | Verification code, service name, validity, "do not share" warning | Marketing, links (on many routes), anything beyond the code |
| Transactional | Order and delivery updates, account alerts, reminders, receipts | Offers, discount codes, cross-selling |
| Promotional | Offers and campaigns to opted-in recipients, with opt-out | Sending without consent, outside allowed hours, to DND-listed numbers |
How to tell the types apart is covered in transactional vs promotional SMS.
Restricted categories
Many operators and countries restrict these categories, sometimes completely, sometimes only with registration or licences:
- Gambling and betting
- Loans, debt collection and debt relief, high-risk financial products, cryptocurrency investment
- Adult content and dating
- Alcohol, tobacco, vaping, cannabis and CBD
- Firearms
- Pharmaceuticals without prescription
- Political and religious messages in some countries
In the United States, carrier and industry guidelines restrict content related to sex, hate, alcohol, firearms and tobacco (often called SHAFT), and some of these are allowed only with age verification. See 10DLC and toll-free SMS in the US.
Country rules that affect content
- Templates: some countries require each message template to be pre-registered, with only variables changing. India's DLT system is the best-known example: see India DLT registration. China requires approved templates and signatures: see China SMS templates and signatures.
- Sending hours: promotional messages are often limited to daytime, and some countries also restrict weekends or public holidays.
- Language: some regulators require local language content or sender identification in the message.
- Consent registries: commercial messages may need a check against a national consent or do-not-disturb list.
Content patterns that trigger filters
- Public URL shorteners: widely used in phishing and often blocked. Use your own domain or a branded short domain.
- Mismatched sender and content: a bank name in the text with an unrelated sender ID.
- Urgent account language ("your account is suspended, click here") that looks like phishing.
- Phone numbers asking to call back to premium or international numbers.
- Unusual characters used to dodge keyword filters, which firewalls treat as a strong spam signal.
Staying compliant
- Declare the traffic type and send real sample messages when you request a route.
- Keep separate templates and, where useful, separate sender IDs for OTP, transactional and promotional traffic.
- Store proof of consent for promotional messages and honour opt-outs quickly.
- Check country rules before launching in a new market; they change often.
- Test new templates on real handsets before a large send, as in how to test an SMS route.
Finding a route that accepts your traffic
When you request A2P SMS routes through VoIPMatcher, include sample content. We source a route from our carriers that accepts that traffic in each country. Request an SMS route.
Frequently asked questions
What does possible carrier filtering mean?
It is a message some SMS platforms show when a text was rejected or never delivered and the operator gave no clear reason. It usually means an operator firewall blocked the message for its content, links, sender ID or volume pattern. Check the content against the route's rules, remove public URL shorteners and confirm the sender is registered.
Can I send links in SMS?
Usually yes, with care. Use your own domain or a branded short domain, since public URL shorteners are widely blocked as a phishing pattern. Many OTP routes accept no links at all, and some countries require URLs to be declared or whitelisted in advance. Test messages with links on real handsets before a campaign.
Why was my SMS blocked as spam?
Common reasons are content that does not match the route's approved traffic type, links through public shorteners, urgent account language that looks like phishing, a sender ID unrelated to the brand in the text, or characters used to dodge keyword filters. Sending without consent or outside allowed hours can also trigger blocking.
Do I need to send sample messages to an SMS provider?
Yes, most suppliers ask for them before opening a route. Sample messages let the supplier check that your content fits the traffic type and the destination's rules, and they are often required for sender ID or template registration. Send real examples, including any links, and keep later traffic consistent with what you declared.
Need a route?
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