SMS Deliverability

SMS spam filters vary heavily from carrier to carrier, and can be changed overnight without warning. This guide is here to give you some background to the process and to help boost your chances of avoiding these filters when sending out SMS in ATMOSai.

How do spam filters work?

If you are hosting a number in ATMOSai, 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. Atmos 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?

7 Tips for Avoiding Spam

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 ATMOSai at this time. If you are looking for a platform that allows for bulk SMS that integrates with Atmos, check out Clicksend. An integration would need to be set up using Zapier.

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, create a Support Ticket by clicking the “?” in the top right corner of the page. ATMOSai 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.

How would I know my SMS has been marked as spam in ATMOSai?

If your SMS was not delivered due to a spam filter, an error icon will appear on the SMS in question. By hovering your cursor over the error, you will be able to see the reason why it failed to deliver. 

If you want to pull up all of the leads with an errored SMS, you can search: