SMS Auto Reply and STOP Keyword Handling
SMS auto reply watches inbound traffic on your own SIM, matches a keyword, and sends a fixed response from the same number. STOP is the special case: it replies and records an opt-out so that person is skipped on the next campaign.
- HOURS
Open 9–6 Sat–Thu. Reply HELP for a person.
- PRICE
Starter plan on the pricing page. Reply STOP to leave this list.
- STATUS
Send your order ID and a person will pick it up in the inbox.
- STOP
You are unsubscribed. We will not message this number again.
Sets suppression immediately
STOP, opt-out, and the legal side
Opt-out handling is not a nice-to-have feature. In markets where commercial SMS is regulated, failing to honour STOP is how programmes get blocked, fined, or both.
Build a deliberate opt-in path too. People who texted STOP once should not reappear because someone pasted an old CSV. If you need help interpreting a specific regulator requirement for your market, talk to counsel; our support team can explain how the product records and applies flags, usually within 24-48 hours of your question.
Auto-reply rules that work versus rules that annoy
A useful SMS keyword response feels like a receptionist. A bad one feels like a chatbot arguing with itself. The difference is almost always in the rule design.
✓ Rules that help
- Keep responses short and specific to the keyword that triggered them
- Always identify your business so the reply is recognisable without a branded sender ID
- Give a clear path to a human — a HELP keyword, a phone number, or a named inbox
- Match common misspellings and local-language quit words you actually see
- Log every auto-reply so you can audit volume and operator cost later
! Rules that annoy
- Auto-replying to your own delivery receipts or status callbacks
- Creating loops where two automated systems keep answering each other
- Replying to short codes, carrier system numbers, or other gateways
- Sending multi-segment essays when one line would answer the question
- Using vague replies like “thanks for your message” with no next step
What SMS auto reply actually does
SMS auto reply is a rule engine sitting on inbound traffic. A message arrives at the SIM in your Android handset, the body is checked against keywords you defined, and when one matches the gateway sends a prepared response from that same number. The customer never notices a queue or a ticket — they just get an answer. Automated SMS replies of this kind cover the questions that repeat all day: opening hours, store address, balance of a prepaid package, or how to reach a person.
STOP is the important special case. When someone texts STOP (or UNSUBSCRIBE, CANCEL, or another opt-out word you map), the system still sends a short confirmation, but it also sets an opt-out flag on that contact. That flag is what keeps the number out of later campaigns. Without it, SMS keyword response alone is only half the job. Pair this with a two-way SMS inbox so staff can still read everything that did not match a rule.
The mechanical detail that matters for cost: every auto-reply is a real SMS on your operator plan. You bring the phone and the airtime; the service fee is based on how many devices you connect and how many messages you send in total. There is no separate “reply credit” pack. If a keyword fires a thousand times in a day, that is a thousand outbound segments on the SIM that received them.
- 01
SMS auto reply matches an inbound keyword on your SIM and sends a prepared response from the same number without a staff member typing it.
- 02
STOP, UNSUBSCRIBE, and CANCEL must set an opt-out flag immediately; that flag is checked before every future send.
- 03
Keyword rules cover the common questions; a webhook lets your own backend decide the reply when the message needs application logic.
- 04
Keep auto-replies short, identify the business, and give a path to a human so customers are not trapped in a loop.
- 05
You supply the Android phone and operator SMS credit; service pricing follows device count and total SMS sent.
Manual replies versus keyword automation
Staff can answer every inbound message by hand. That works until the volume climbs, the shop closes overnight, or STOP texts sit unread while the next campaign goes out.
Handling every inbound message by hand
- Overnight and weekend messages wait until someone opens the inbox
- Answers vary by who is on shift, so customers get inconsistent facts
- STOP and opt-out texts are easy to miss when the queue is long
- Opt-outs recorded late — or not at all — leak into the next bulk send
- Staff time is spent on HOURS and PRICE instead of real complaints
Keyword rules with automatic replies
- Matched keywords get a prepared, consistent reply from the same SIM
- STOP sets the opt-out flag at arrival, before the next campaign runs
- Staff only see unmatched messages and anything you mark for escalation
- Opening hours and stocked FAQs stop competing with refund tickets
- The same rules fire whether the shop is open or closed
Automation does not replace judgement. It removes the repetitive layer so people can spend time on the messages that need it. If your inbound mix is mostly unique conversations, lean on the inbox. If half the traffic is the same five questions, keyword rules earn their keep on day one.
Setting up keyword rules that people will actually use
Start from real inbox history, not from a brainstorm of every possible question. Six steps cover the setup most teams need.
- 01
List the questions you actually receive
Pull a week of inbound traffic from your inbox or support desk. Group the repeats — hours, pricing, address, tracking status — and ignore one-off complaints that need a person. Keyword automation only pays off on patterns that show up often. - 02
Choose short, unambiguous keywords
Prefer single tokens such as HOURS, PRICE, STATUS, or HELP. Avoid phrases that customers will mistype. If two meanings could collide, pick a rarer word rather than hoping people will send the longer phrase every time. - 03
Write the response inside one segment
Keep the reply under 160 GSM-7 characters when you can. State the answer, name your business, and offer a path to a human. Long multi-segment auto-replies burn operator credit and feel like spam even when the content is useful. - 04
Define the fallback for unmatched messages
Decide what happens when nothing matches: a short “we got your message” acknowledgement, silence plus an inbox flag, or a hand-off to staff. An empty fallback is fine; an endless “sorry, try again” loop is not. - 05
Decide what escalates to a human
Complaints, refund requests, and anything mentioning a specific order ID should skip the keyword engine and land in the inbox for staff. Automation handles the catalogue; people handle the exceptions. - 06
Test from a real handset
Send each keyword from a phone that is not the gateway device. Confirm the reply text, the timing, and that STOP actually sets the opt-out flag before you point production traffic at the rules.
After go-live, review unmatched traffic once a week. New keywords should come from phrases you see repeatedly, not from guesses. The acceptable use policy also sets boundaries on what kinds of automated traffic belong on the platform.
Wiring SMS auto reply into your own backend
Keyword rules cover the common cases without code. When the answer depends on an order ID, a balance, or a CRM lookup, receive the inbound event on a webhook and let your application decide. The developer center documents the same send path used for ordinary outbound traffic.
# Inbound webhook (message.received)
{
"id": "evt_01K2F8QW3N4RXB7M",
"type": "message.received",
"createdAt": "2026-08-12T14:04:09Z",
"apiVersion": "2026-08-12",
"data": {
"message": {
"id": 41822,
"number": "+14155552671",
"text": "Yes, please reschedule to Thursday.",
"status": "Received",
"deviceId": 3,
"receivedAt": "2026-08-12T14:04:09Z"
}
}
}
# Reply from your backend when keyword rules are not enough
curl -X POST "https://app.sms-gateway.app/api/v1/messages" \
-H "Authorization: Bearer $SMS_GATEWAY_API_KEY" \
-H "Content-Type: application/json" \
-d '{"to":["+14155552671"],"text":"Done — Thursday 10:00 confirmed. Reply STOP to opt out.","type":"sms","campaign":false}'Treat replies as idempotent operations. Webhook deliveries can repeat when your endpoint times out or returns a 5xx. Key the send on something stable — device ID, sender, timestamp, and message body hash — and short-circuit if that key already produced a message ID. Pair the flow with delivery reports when you need to know whether the auto-reply itself reached the handset.
Regional notes on keywords and opt-out
Opt-out wording, language, and promotional limits change by market. English STOP is a start, not a complete dictionary.
United States
Opt-out expectations are strict. STOP, UNSUBSCRIBE, CANCEL, and similar words must be honoured immediately, and the suppression list must stick across later campaigns and imports.
India
DND registration and template rules shape what you can send. Keyword replies that look promotional can still fall under local limits even when the customer initiated the exchange.
Bangladesh
Customers often write keywords in Bangla or mixed script. Mirror the common local spellings as separate rules, and remember Unicode replies cost more segments on the operator plan.
Nigeria
English STOP is not always what people type. Add local-language quit words you actually see in the inbox, and keep a human path for messages that do not match cleanly.
Browse more markets on the SMS gateway by region hub when you expand beyond these four.
Related features on the same fleet
These run on the same phones, the same account, and the same REST SMS API— no extra product silos.
USSD Gateway: Run USSD from an API
Trigger USSD codes such as balance checks and read the operator response back through the API.View feature →Two-Way SMS: Replies on Your Own Number
Keep the conversation on the number you sent from and route replies into your systems.View feature →Bulk SMS from Excel & CSV
Upload a spreadsheet, map your columns, and personalise every message from your own data.View feature →Common questions about Auto-reply & STOP
Straight answers for teams evaluating this feature for production OTP, bulk, or two-way traffic.
Run auto-reply & stop on your own SIM
Install the Android app, pair a device with operator SMS credit, and test this feature in the panel or over the API. Paid plans are metered by devices and SMS send volume.