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Why was my message undelivered?

There are many reasons why a SMS message is undelivered. The most common reasons are:

Invalid number

The number you’re sending to is invalid. Verify that the number is correctly formatted and doesn’t include any invalid characters. A properly formatted number will start with a country prefix (without leading zeroes or plus signs) like so: 46736007500.

What is a country prefix?

A country prefix is the first part of a number that decides on which country the message will be sent to. Example: 46736007500 is a number where 46 is the country prefix that stands for Sweden.

Absent subscriber

This means that the subscriber is not connected to the network and therefore the operator can’t deliver the SMS. The most common cause for being absent is that the handset is switched of, but it could also be that the subscriber is out off network reach, have bad signalling etc.

Handset Cannot Receive SMS

The most common reasons are; the memory of the handset is full, technical errors at the moment of delivery or that the subscriber does not have SMS enabled, a call barring.

Signalling issue

This implies Signaling between SMSCs fail to connect with each other. It could be one of the SMSCs has a firewall or blocking SS7 signal and hence messages are not delivered.


During high throughput processing scenarios, as may be common in online transactional processing (OLTP) architectures, a throttling controller may be embedded in the application hosting platform to balance the application’s outbound publishing rates with its inbound consumption rates, optimize available system resources for the processing profile, and prevent eventually unsustainable consumption. Basically you are sending in a faster speed than you are allowed to do with your account.

Invalid sender ID (filtering)

When you experience Invalid Sender ID it can mean that Some operators have put up restrictions to allow certain format of sender ID to be used, such as numeric sender ID, alpha numeric sender ID or short code sender ID. When a wrong format of sender ID has been used, it will be undelivered due to invalid sender ID.

Missing destination in price list

The destination you’re trying to send to does not exist in your current price list. Please contact your account manager to have them add the destination.

This error will generate a delivery report with status rejected and error code 711.

Carrier Spam Filters

Mobile Operators wants to protect their subscribers from spam, fraud and other unsolicited messages. They do this by implementing Spam Filters which will regulate the inflow of messages to their network. Due to the complexity and at the same time simplicity of a text message, this filtering is often very crude and it’s not unusual that legitimate texts will be blocked also.
This filtering will also work to protect their own revenue by forcing A2P traffic to be directed to their own sales department.

Since operators can filter exactly how they want and when they want, and even change how they filter (which variables they will filter on) at any time, all we can do is to provide you with any information we might have to help you bypass any filters.

When a filter is installed at any destination Network Operator this applies to that Operator’s network and works in any way the Carrier want.

This is:
1) Affecting all SMSC’s, thus a fail over option do Not solve a filtering issue.
2) Have a market wide affect.
3) Is triggered by the sending parties traffic, trigger(s) may be, e.g.;
a) Alphanumeric Sender ID
b) Numeric Sender ID with triggers as ex;
b1) Starting with local country prefix
b2) Too few digits
b3) Too many digits
b4) Including any string of digits that the Operator wish to filter
c) Content, any words or combinations of words/characters/numbers that the Operator wish to filter
d) Bulk, the filtering can drop messages as per configuration, e.g. if more than one identical message is sent.
e) Flooding: filtering may drop messages if more than one identical message is sent to the same number
f) Delivery report, the Operators are in full control of their filtering and their network, thus they can choose to reply with “Delivered” even when they are dropping the messages. You can read more on False DLR filtering here.

Please note that what we offer is signaling to a network: it is up to the client to monitor and adjust their traffic in response to any filters.

To get traffic delivered in a filtered network the Client need to run simulations and tests, with the above in mind, and verifying delivery before sending. Sent bulks need to be monitored since the filter can change at any time per the Operator’s will.

In short, the filtering is on the destination Network Operator side thus the Sending SMSC cannot influence this in any way.

To improve your delivery;
1) Test, monitor and adjust your traffic.
2) Buy direct from the affected Operator at a higher cost.

We have high daily traffic to the mentioned Network, and clients who commit to get delivery follow the above steps and adjust as the filtering change,
– this way keeping delivery up at a below market cost.


Roaming means that the handset is not connected to its home network but to another network, most often in another country, i.e. a “roaming number” is a number/handset that is abroad. As soon as a number is not inside its home operator network, reachability will be dependent on roaming agreements between operators or the SMSC reach to the network where the handset is currently roaming. Shortly put: we can never ensure that an SMS to a roaming number will deliver.

Portability Failures

This could arise due to failures during  Mobile number portability.

Updated on October 28, 2016

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