Phone System · 1 min read
Error 21610: Attempt to Send to Unsubscribed Recipient
What this error means
Error 21610 means the recipient has opted out of messages from your number, so sending is blocked. This usually happens after the contact replies STOP or another opt-out keyword, or when Do Not Disturb (DND) is enabled for SMS or all channels on the contact.
The block protects the recipient's preferences and keeps you compliant with consent rules.
Common causes
- The contact replied STOP or another recognized opt-out keyword.
- DND is enabled for SMS or for all channels.
- The number was reassigned to someone who previously opted out.
- A workflow or campaign is sending to a contact who withdrew consent.
How to fix it
- Open the contact and check the conversation for STOP or another opt-out reply.
- Review the contact's DND settings.
- Do not try to work around the opt-out. Only resume texting if the contact opts back in.
- To opt back in, the contact can reply START (or another supported opt-in keyword) from their phone. After they do, you can turn off DND for SMS on the contact.
- Send your next message only after the opt-in is confirmed.
Prevent repeat errors
- Add a DND check or filter before SMS steps in workflows.
- Remove opted-out contacts from SMS campaigns and smart lists used for texting.
- Give contacts another way to reach you, such as email, if they no longer want texts.