In most countries, you must let contacts opt out of marketing SMS messages. If a contact changes their mind, they can opt back in themselves, or you can resubscribe them using the API.

Some service providers or mobile devices treat short codes as premium rate numbers. If a contact has a network block for premium numbers, their opt-out SMS won't work, and it shows as not sent for that contact.

For Android users, a message saying This may cause charges to your mobile account might appear when sending SMS messages to five-digit numbers.

To unsubscribe with a shared short code, contacts reply or send an SMS to your short code with the keyword, a space, then a designated word such as STOP. For example, if your keyword is COMPANY, a contact sends COMPANY STOP to your short code to opt out.

Contacts are only opted out if the opt-out word directly follows the keyword and space, that is KEYWORD OPTOUTWORD. If any other characters come before the opt-out word, the opt-out won't work.

A long number is dedicated to your company, so you don't need a keyword for contacts to unsubscribe from your SMS campaigns.

To opt out with a long number, contacts send an SMS message to your long number with an opt-out word. The opt-out word must be the first word in their response for the opt-out to work.

In certain regions, you can let contacts unsubscribe by clicking a personalised link in a message you've sent them, instead of sending an SMS.

You can create a customised unsubscribe form to allow contacts to opt out of your SMS marketing.

STOP is the most common opt-out word, but there are six possible opt-out options:

To resubscribe to your SMS campaigns with a shared short code, contacts can either:

For example, if your keyword is COMPANY, a contact sends COMPANY START or COMPANY UNSTOP to opt back in.

Since a long number is dedicated to your company, you don't need a keyword for contacts to opt back in. To resubscribe with a long number, a contact can reply to an older SMS campaign you sent before they opted out.

Auto-responder keywords don't process resubscribes

It's not currently possible to resubscribe using a keyword configured as an auto-responder. If a keyword is linked to an auto-responder, it won't process a resubscribe action for opted-out contacts. Use a keyword that isn't tied to an auto-responder, or rely on standard opt-in words like START or UNSTOP sent directly to your long number.

As well as contact-initiated opt-ins, you can resubscribe a contact to SMS through the Contacts API. Set the SMS channel status to subscribed in your contact update request, and the contact's SMS subscription is restored.

You can set the status using Import a single contact, Import contact collection, or Replace a contact.

For a straightforward resubscribe, use Import a single contact. It updates only the fields you pass. Replace a contactoverwrites the entire contact record, so use it only when that's what you intend.

US toll-free numbers stay blocked at the network level

For US toll-free numbers, networks unsubscribe contacts at the carrier level when they send a stop message. Even after you set the status to subscribed through the API, these contacts won't receive messages until they text a start keyword themselves. For these numbers, rely on keyword resubscription rather than the API.