# Two-Way SMS: Replies, Keywords and Opt-Out | ZafeConnect

> How to design two-way SMS: numbers that can receive, keywords such as STOP and YES, routing replies to the right system and handing over to a person.

Canonical URL: https://www.zafeconnect.com/blog/two-way-sms-replies-keywords-opt-out
Language: en
Last modified: 2026-11-09

## Two-way SMS: designing replies, keywords and opt-outs

URL: https://www.zafeconnect.com/blog/two-way-sms-replies-keywords-opt-out

Published: 2026-11-09

The moment people can answer, a notification becomes a conversation. That is useful, and it needs a little design so that replies end up in the right place.

Key takeaways:
- Replies need a number that can receive messages, not an alphanumeric sender.
- Keywords such as STOP, HELP and YES give people simple controls; accept spelling variations and local words.
- Route each reply to the right system with the context of the message it answers.
- Hand over to a person when the automation cannot help.

### Start with a number that can receive
People cannot normally reply to an alphanumeric sender name. For two-way messaging you need a number that can receive texts, such as a long number or, in some countries, a short code. The choice and the availability differ by country, as our article on sender types explains.

### Keywords people actually type

- STOP to opt out, handled at once and for every system
- HELP for contact information
- YES, NO or a number such as 1 and 2 for confirmations
- Accept lower case, extra spaces and punctuation
- Accept local words too, for example STOP, STOPP, AFMELD, JA and NEJ in Danish

### Route replies with context
A reply is only useful if you know what it answers. Match the reply to the latest message you sent to that number, and pass both to the right system: a booking system for confirmations, a support inbox for questions, a bot for simple requests.

Your provider normally delivers inbound messages to a webhook or an API. Design that endpoint like any other: respond quickly, process in the background and expect duplicates.

### Hand over to a person

- Offer a clear way to reach a human
- Tell people what to expect, for example office hours
- Pass the conversation history on to the person who takes over
- Keep automated replies short and honest about being automated

### Common mistakes

- Asking for a reply from a sender that cannot receive
- Ignoring spelling variations and local-language keywords
- Handling STOP in one system but not in the others
- Letting replies pile up in an inbox nobody reads

### How ZafeConnect fits
ZafeConnect offers 2-Way Messaging and phone numbers as products, with webhooks for events. Tell us your countries and use cases and we will confirm which numbers and keywords apply.

FAQ:
Q: Can people reply to an alphanumeric sender?
A: Usually not. Use a number that can receive messages if you want replies.

Q: What happens when someone replies STOP?
A: You should stop sending marketing messages to that number at once, in every system that can send to it.

Q: How do I receive replies?
A: Through a webhook or an API from your provider. Respond quickly, process the message in the background and handle duplicates.