If your business sends SMS — order updates, appointment reminders, offers — you may have seen messages with links suddenly stop reaching customers, or your SMS provider asking you to "whitelist your URLs". This guide explains, in plain language, what changed, why short links are affected, and how to send links that get through.
First, a quick DLT refresher
In India, business SMS runs on DLT (Distributed Ledger Technology) platforms operated by the telecom companies, under rules made by TRAI, the telecom regulator. To send commercial SMS, a business (called the principal entity) registers on a DLT portal and then registers:
- Headers — the sender name customers see, like
SHRMSW, also called the Sender ID. - Content templates — the approved text of each message, with variable parts marked.
- Consent — for promotional messages, proof that people agreed to receive them.
Your SMS provider (the telemarketer) sends messages on your behalf, and the operator checks each message against what you registered. If something does not match, the message can be blocked. This checking is called scrubbing.
What changed for links
Operators now also check the links inside messages. A link in a template — sometimes called a CTA (call to action) — has to be whitelisted on the DLT platform for your entity. Messages with links that are not whitelisted can be blocked during scrubbing.
Industry guides from SMS platforms give 1 October 2024 as the compliance deadline for this (industry guide). Another platform guide puts it simply: all URLs in SMS campaigns must be pre-approved and whitelisted on the DLT platform, or messages may fail (industry guide).
Why short links get extra attention
Short links are popular in SMS because they save characters and let you count clicks. But they also hide where they go, which is exactly what scammers want. A public shortener domain is shared by thousands of senders, honest and dishonest, so whitelisting "the shortener" would whitelist everybody.
That is why the guidance on short links is stricter. One industry guide quotes the rule this way: senders should not use any URL shortening service or short URLs "unless the shortened URL clearly indicates that it has a relation with the Sender." In practice, platforms do this by putting the Sender ID inside the short link — for example https://short.domain/SENDERID/abc123 — and whitelisting that pattern separately for each Sender ID.
So if your messages use a random public short link, there is a good chance operators will not accept it, even if the website it opens is perfectly fine.
How to send links that pass
- Decide which domain your SMS links will use. Your own website domain is the simplest. If you want short links, use a short-link format that includes your Sender ID, or a short domain you control.
- Whitelist it on every DLT portal you use, for every Sender ID that will send it. If you send through more than one operator or provider, each may need its own entry.
- Register templates that match exactly. The link format in your registered template should match the link in the message you send. Ask your provider how they want variable parts of the link marked.
- Prefer clean https links. Avoid links that bounce through several other websites, and keep query strings (
?utm_source=…) only if your provider confirms they are accepted — some operators ask for the long form of such links to be whitelisted. - Test before the big send. Send a small batch to phones on different networks and check that every message arrives and every link opens.
- Keep a record. Note which domains and patterns are whitelisted on which portal, and for which headers. When a campaign fails, this is the first thing your provider will ask for.
Do not forget message length
A link uses up characters in your SMS. A single SMS holds 160 characters in plain English, but only 70 if it contains Hindi or other Unicode characters. Go over and the message is split into parts, each charged separately. Check your final text, link included, with the free SMS length counter before you register the template.
Where hi4.in fits
- Today: ordinary hi4.in links (like
hi4.in/abc123) do not contain your Sender ID, so operators may not accept them in DLT templates. Ask your SMS provider before using them in SMS. - Coming soon: SMS links in the Sender ID format,
hi4.in/SENDERID/offer, with click reports per campaign, bulk creation and an API. You can join the waitlist on the SMS Links page. - Free tools now: paste a message into the SMS link DLT checker to spot common problems, and count characters with the SMS length counter.
We will never promise that a message will be delivered — that decision belongs to the operators. What we can do is make links that follow the published format and are easy to whitelist.
Quick answers
Does this apply to WhatsApp messages?
No. DLT and SMS link whitelisting apply to SMS. WhatsApp Business messages follow WhatsApp's own rules.
Do I need to whitelist links in OTP messages?
If the message contains a link, assume yes. Better still, keep OTP messages free of links — customers are rightly suspicious of OTP messages with links.
My messages with links are failing. What do I check first?
Ask your provider for the failure reason. Then check that the exact domain is whitelisted on the right portal, for the right header, and that the link in the message matches the registered template.
For the short version, see our help article Using short links in DLT-registered SMS.