# Sender IDs

A sender ID is whatever the recipient sees in the *from* position: a short name, a full telephone number, a short code, or a toll-free number. The choice decides whether anyone can reply, where your reputation accumulates, and whether you need to register in advance. Connect presents the business's own line on outbound calls rather than the individual's.

- **Status:** Reference
- **Audience:** both
- **Channels:** sms, phone
- **Last verified:** 2026-09-10
- **Canonical:** https://connectbyjbrh.com/docs/technology/sender-id/

## Four kinds of identity, with different trade-offs

| Kind | Looks like | Can be replied to? | Usual constraint |
|---|---|---|---|
| Alphanumeric | A short name in place of a number | **No** — it is not routable | Pre-registration in many markets; not permitted in some |
| Long code | An ordinary telephone number in international format | Yes | Throughput limits; reputation is per number |
| Short code | A five- or six-digit number | Yes | Application and approval; the heaviest to obtain |
| Toll-free | A national toll-free number | Yes | Verification of the business behind it |

The first row is the one businesses reach for and it has the sharpest consequence, which the table understates by putting it in one word.

## A name cannot be replied to, and that changes your opt-out

An alphanumeric sender is a display string, not an address. There is nothing behind it to receive a message, so a recipient who replies STOP gets a failure or silence. If your opt-out route is *reply STOP* and your sender identity is a name, you have published an instruction nobody can follow.

The usual answers are to send from a number instead, to carry the opt-out route inside the message text, or to run the two in parallel — a name for notification traffic and a number wherever a conversation is possible. What is not an answer is leaving the instruction in place and treating the absent replies as consent. See [STOP and opt-out keywords](/docs/technology/stop-keyword/).

> **Note** Two-way messaging always needs a number. A design that assumes replies will arrive should settle its sender identity before it settles anything else.

## Reputation attaches to the identity, not the campaign

Every complaint, block and non-delivery accumulates against the identity that sent the message. That is the whole reason the choice matters commercially rather than aesthetically.

- **A shared identity pools your reputation with strangers.** Somebody else's campaign degrades your delivery, and you have no visibility into who they are.
- **A dedicated identity isolates it, and makes it yours to ruin.** The upside is control; the downside is that there is nobody else to blame.
- **Reputation does not transfer.** Moving to a new sender identity starts at zero, which is a cost, not an escape.
- **On WhatsApp the equivalent is the number's quality rating**, and the display name goes through review. On email the equivalent is domain reputation, governed by [DMARC](/docs/technology/dmarc/) and its relatives.

## Does Connect use sender IDs?

**Used on voice, and prepared for on SMS.** On calls, the identity presented is the business's line rather than the person placing the call. When somebody dials from the browser softphone, the handler matches them against the workspace's own softphone routes, checks that the call may be placed at all, and then dials with the business's caller identity attached — so the customer sees the company, and a call-back reaches the company rather than one colleague's browser.

Number ownership is a checked fact rather than a typed setting: a line is a row in `channel_routes` carrying its provider, its assignment and its inbound and outbound permissions, and the permission check runs inside the workspace that owns the row.

On SMS the sender identity in India is the registered header, and Connect holds that registration data without being able to perform the registration — see [DLT registration](/docs/technology/dlt/). Since outbound SMS itself is foundation and the live carrier carries none, no sender identity is in use for messaging on that account today.

## Changing one costs more than it looks

1. Check what breaks on the recipient's handset.
   - Result: A new sender identity starts a new thread. Your message appears detached from every previous one, and a customer looking for the earlier reference will not find it under the new name.
2. Check what breaks in your own records.
   - Result: Suppression held against a sender identity rather than a person does not follow the change — which is one reason to hold it against the person.
3. Check what has to be re-registered.
   - Result: In a market with a registry, a new header means new registrations and, where templates are bound to a header, new template approvals.
4. Check what recognition you lose.
   - Result: Consistency is most of what makes a message look legitimate to the person receiving it. Rotating identities is a pattern associated with senders nobody wants to hear from.

## Questions

### Why can a customer not reply to our messages?

Because the sender identity is a name rather than a number. Alphanumeric senders are display-only and have nothing behind them to receive a reply. If replies matter — and they usually do, if only for opt-out — send from a number.

### Whose number does a customer see when a colleague calls from the browser?

The business's. The outbound call is dialled with the workspace's own caller identity after a permission check against the line, so a call-back reaches the business rather than one person's browser session.

### Can we use the same sender identity in every country?

Generally not. Rules differ by market: some require registration, some do not permit alphanumeric identities, and some replace what you send with something of their own. Sender identity is a per-market decision.

## Related

- [DLT — Distributed Ledger Technology registration in India](https://connectbyjbrh.com/docs/technology/dlt/)
- [SMS](https://connectbyjbrh.com/docs/technology/sms/)
- [STOP and opt-out keywords](https://connectbyjbrh.com/docs/technology/stop-keyword/)
- [Proving a phone number belongs to a workspace](https://connectbyjbrh.com/docs/security/number-ownership/)
- [Calling from the browser](https://connectbyjbrh.com/docs/phone/softphone/)
- [DID — a direct inward dialling number](https://connectbyjbrh.com/docs/technology/did/)
- [Email deliverability](https://connectbyjbrh.com/docs/technology/deliverability/)

## What this page is based on

- `docs-source/sources/CHANNELS.md` §3 — sender headers and DLT
- `docs-source/sources/PHONE.md` §11 — the softphone and caller identity
- `docs-source/sources/PHONE.md` §1 — channel_routes and line permissions