Ensuring your outbound SMS messages are delivered successfully
Use long codes for unique messages only
Long code SMS is intended for person-to-person (P2P) communication or application-to-person (A2P) use cases where a human is initiating the message. The message should contain content that is specific to the recipient.
Types of messages that are good candidates for long codes:
An SMS chatting application where a customer is communicating with a sales or customer service representative
An SMS reminder about an upcoming appointment with a doctor
A notification that a taxi has arrived
If the content you are sending is not unique to the customer then it's likely a marketing campaign which is better suited for short code messaging.
Limit your send rate
Mobile operators generally only accept 10 messages per minute from any long code number (that's no more than a message every 6 seconds). The rule of thumb is that the rate shouldn't exceed what a human could reasonably do if they were using a phone. Please keep in mind, your overall Telnyx portal account is limited to sending 1 message / second. If you require a higher limit, please reach out to firstname.lastname@example.org via email, and we can talk about raising your message rate limit. If you attempt to send more quickly than 1 message / second overall or more than 10 messages/minute/number, Telnyx's SMS platform will throttle your deliverability so as not to exceed the maximum rate.
Don't send a high volume of messages from consecutive numbers
You may want to purchase and use a consecutive number range to send long code messages. However, SPAM filters used by mobile operators identify this as suspicious and are apt to block these messages. Telnyx recommends that you purchase discontiguous numbers if you plan to send a higher volume of messages.
Limit the length of URLs in the message
Lengthly URLs may not only cause your messages to be split into multiple parts (and being charged accordingly) but also are more likely to be flagged by SPAM filters. If your URL is more than 50 characters we recommend that you use the URL shortener that we provide under the settings of the messaging profile. More info on this feature here.
Update 31st December 2020: The above feature is no longer being made available but a newer customer domain whitelisting feature will be released in 2021.
Be careful when sending multi-part messages that also have a URL. If you don't know the length of the URL beforehand (since you may be dynamically creating it) try to minimize the rest of the text in your message to leave room for the URL.
You should certainly consider the type of url domain you use, since there are URLs which are known to be related to spam or are often attributed to fraudulent activities. Take a look at some domains & keywords that we've seen regularly caught in messaging filters industry wide no matter the number type being used.