Delays in message delivery
There are a number of reasons why delivery of an SMS message might be delayed.
While it would be very difficult to provide an exhaustive list of reasons for a delay, as some reasons are technically complex and are not always explained by the operators, we can outline some of the reasons that you might see occasionally affecting your sends.
Reason | Description |
Handset temporarily unavailable For example, due to loss of signal. | The most common cause of delays in message delivery due to the handset not always being readily available.
This usually happens when the user is travelling in more remote areas or when the network signal isn’t strong enough. |
Handset is assigned to a new base station | Handsets and Short Message Service Centres (SMSCs) constantly ping each other to determine the handset and service centre status.
As part of its operation, the SMSC needs to determine where the handset’s closest base station is. During times of switching from one base station to another, message delays can occur. |
SMSC and base stations retry schedules | Depending on the volume and activity load of the base station, certain messages might take longer to be delivered than others.
There’s no prioritisation on delivering particular messages, but the more often a message is retried, the longer the time interval is before the next retry is attempted until the message ultimately expires. |
SMSC and base station reliability | If a base station fails for any particular reason, SMSC’s automatically reroute all messages through the next closest base station.
This results in the surrounding base stations dealing with increased activity and volume, causing in considerable delays in message delivery for that area. This scenario rarely occurs. |
Duplicated messages
In most cases, duplication of messages occurs when handsets are on the edge of reception and fail to send an acknowledgement that a message has been successfully received and so the message is retried.
There are a number of things that recipients can try to resolve the issue of duplicated messages:
Move to an area where reception is better.
Reconnect the device to the mobile network by switching in and out of flight mode.
Try their SIM card in another phone to eliminate handset issues.
Switch from 5G or 4G to 3G or 2G as these have a greater reception range.
On pay-as-you-go devices, it can sometimes help to disable the re-enable balance notifications.
On rare occasions, duplicate messages can be caused by a fault on the network.
If you’re still receiving reports of duplicate messages and the above steps aren’t helping, contact Support.
It’s possible that duplicate messages are multiple submissions of the same message caused by errors in a CMS system, web service, or API integration that we can help you to resolve.