1. Invalid Numbers
This is the most common reason that text message delivery can fail.
If a text message is sent to an invalid number, it won’t be delivered – similar to entering an incorrect email address, you will get a response from your phone carrier informing you that the entered number was invalid.
There can be quite a few reasons for this. For example, all messages being sent to U.S. telephones must begin with the country prefix “1” – if the international country prefix is not added, the message may fail to deliver correctly.
Other causes of invalid numbers include attempting delivery to landlines – landlines cannot receive SMS messages, so delivery will fail.
And, of course, SMS messages may fail if an individual’s phone number is incorrect, disconnected, or otherwise invalid.
2. Carrier Filters
Similar to email, some cell phone carriers have implemented filter systems that can block spam, phishing attempts, and other unwanted messages.
One of the primary ways that carriers block spam is by separating “A2P” and “P2P” messages.
P2P messages are messages sent between individuals – and they always have a valid alphanumeric sender ID.
These messages are likely to be delivered without being filtered.
A2P messages are messages sent from mass texting applications. Some carriers will “filter” these messages, and prevent them from being sent to individuals, in an attempt to prevent spam.
To avoid this, DialMyCalls uses advanced A2P routing to send messages through A2P-enabled routes.
However, some messages may still be blocked if they contain certain keywords, though this depends on the specifics of each individual’s carrier.
3. Routing Factors
SMS routing can be a large factor in the successful delivery of a message.
While most SMS messages are sent through routes directly to the relevant phone numbers, this is not always the case.
Some SMS messages may be sent to a particular network provider that does not allow the delivery of a message.
If that network provider doesn’t provide automatic rerouting services, the delivery of the message can fail entirely.
Despite the fact that most U.S. telecom providers cooperate to route SMS messages, this situation can still occur and is a common cause of text messages not being delivered properly.
4. Incorrect Encoding
SMS encoding is what determines the allowable combination of characters that can be sent.
Messages are usually sent using Unicode, which contains 70 characters, or GSM 3.38 – a global standard that allows for 160 characters.
In the U.S., Unicode is the standard encoding method for SMS messages.
Messages which are sent using GSM 3.38 may be mangled or unreadable when sent – and some carriers may refuse to deliver these messages entirely.
To avoid SMS delivery failure, ensure that your SMS messaging service or carrier is using Unicode in the U.S.
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