SMS Deliverability

SMS in Close may not deliver for a number of different reasons. Most commonly this would be when you are trying to send an SMS to a number that is not SMS-enabled (such as a landline), or if your content was marked as spam by the receiving phone carrier.

You will notice an error on the SMS activity if our provider Twilio is letting us know that the message was undelivered. By hovering your cursor over the error message, you will see the reason why it was undelivered.


Below are the most common error messages you will see with your undelivered SMS messages:

  • Error 30005 "Message Delivery - Unknown destination handset": The destination carrier is reporting the To number is unknown, or no longer in service.
  • Error 30003 "Message Delivery - Unreachable destination handset": The destination carrier is reporting the 'To' number is unreachable - the device is likely powered down, out of the service area, or may not accept your messages.
  • Error 30007 "Message Delivery - Carrier Violation": The destination carrier is filtering out your messages for delivery. The content of your message was flagged as going against carrier guidelines.
  • Error 30008 "Message Delivery - Unknown error": The destination carrier has returned a generic error message.
  • Error 30004 "Message Delivery - Message blocked": Your message has been blocked from reaching the destination.
  • Error 30006 "Message Delivery - Landline or unreachable carrier": The destination is a landline phone, or the destination carrier can't be reached.

For a more detailed breakdown of the specific error message you are seeing, as well as some tips to troubleshoot you can head over to Twilio's SMS troubleshooting guide here -

How do spam filters work?##

Spam filters vary heavily from carrier to carrier, and can be changed overnight without warning. If you are hosting a number in Close, SMS is taken care of by our provider, Twilio. SMS can be marked as spam by Twilio's carriers or the receiving leg’s carrier. Algorithms and systems will be scanning SMS for certain keywords, SMS length and other criteria that may come across as ‘spammy’ in nature and block them before they are delivered.

One SMS that you sent to a customer may deliver as expected today and the exact same message to another customer may be flagged as spam tomorrow. Close has no control over these filters and they are incredibly volatile. So keep reading for some more insight!

What is the difference between a long code and short code number?##

There are two types of number when it comes to SMS, long code and short code, and these have different rules when it comes to limitations.

Long Code:
“Long codes are regular phone numbers that can make/receive Voice calls as well as SMS messages. Long codes are meant for conversation Person-to-Person (P2P) communication. Long-codes are not recommended for one direction bulk messaging use cases.”

Short Code:
“A Short Code is a 5 or 6-digit number (e.g., 12345) used to send and receive SMS messages from mobile phones. Short Codes are allowed for application to person (A2P) communication, which is why businesses who need to communicate to customers on a large scale can only use Short Codes (i.e., not Long Codes)”

We do not support the use of short code numbers in Close at this time. If you are looking for a platform that allows for bulk SMS that integrates with Close, check out Clicksend. An integration would need to be set up using Zapier. Get started here.

7 Tips for Avoiding Spam##

Below you will find some tips and tricks from our provider to maximize your chances of avoiding spam filters on long code numbers:

  • Keep each SMS to less than 160 characters (1 unit of SMS). If you exceed 160 characters, the SMS sending velocity jumps above the 1SMS/2 second threshold.
  • If you are using emojis or any non-unicode character that falls outside of the GSM-7 character set, try to keep your SMS to 70 characters or below.
  • Try to avoid LOTS OF CAPITAL LETTERS, exclamation marks !!!!!!, and keywords that could trigger any alarm bells - “free”, “promotion”, “Limited Time”.
  • Avoid sending out the same/similar content to multiple numbers in a short space of time.
  • Avoid using repetitive URL's and keywords, especially shortened links (such as
  • If the ratio of incoming to outgoing SMS exceeds 1:3, you will be more likely be flagged.
  • Do not send more than 200 SMS within a 24 hour period

If you are avoiding all of the above and notice your number is still being flagged as spam, reach out to [email protected] for next steps. Close does not control spam filters but we can loop in our telephony provider to give a more concrete reason why the SMS was blocked and point you in the right direction.

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