Short answer
Business SMS is usually blocked because of an unregistered sender ID, a grey route, a shared link shortener, scam-like wording, missing opt-out text or a sudden jump in volume. Operator firewalls, content filters and the phone itself each judge the message, and it must pass all three. Most causes can be fixed by the sender, in the order registration, route, content, consent, volume.
Which layers filter your messages?
| Layer | Looks at | What you can change |
|---|---|---|
| Operator firewall | Sender ID registration, route, volume patterns | Register senders, use direct routes, warn your provider before spikes |
| Content filter | URLs, keywords, templates, opt-out text | Rewrite copy, use your own link domain, include opt-out |
| Handset filter | Sender novelty, user history, link checks | Reputation and consent only |
What are the most common causes?
- Sender ID not registered where required, such as the UAE, Saudi Arabia or India DLT.
- A grey route that firewalls are built to catch.
- A public link shortener shared with spammers.
- Phishing-style wording such as urgent threats or verify-now links.
- No sender identity or opt-out.
- Volume jumping with no warning, or near-identical messages from many numbers.
How do you diagnose and fix it?
- Group the last seven days of delivery reports by operator, sender ID and campaign.
- Look for one operator at a fraction of normal delivery, which points to an operator-side rule.
- Send a short plain message with no link to test handsets on that operator.
- Test your own short-link domain against the shortener.
- Ask your provider for operator-level error codes.
- Fix in order: registration, route, content, consent, volume, and keep OTP traffic on its own sender.