FAQ: Why Didn’t I Receive an SMS Notification?
Our platform relies on global SMS networks to deliver time-critical travel risk and safety notifications. While SMS is a widely used communication channel, it is not a guaranteed-delivery technology. Delivery issues can occur for a variety of reasons outside our control. This FAQ explains the most common factors that may prevent an SMS message from reaching a recipient.
1. Differences Between Mobile Operators
SMS delivery varies across countries and mobile network operators. Each operator may use different delivery routes, prefix rules, infrastructure, and filtering mechanisms. Because SMS can travel through multiple intermediaries, its behavior is not fully standardised worldwide.
In addition, many of these filtering mechanisms exist to combat SMS spam, which is a major problem in the A2P (Application-to-Person) messaging ecosystem. Since A2P messages are sent from software or platforms—not from one person to another—operators apply strict controls to protect subscribers from fraud, phishing, and unsolicited messaging. While these filters improve user safety, they can also unintentionally delay or block legitimate messages.
2. No Guaranteed Delivery
SMS technology does not include a built-in delivery guarantee. Some networks do not return Delivery Reports (DLRs), making it impossible to confirm whether a message reached the device. This means that even if a message was sent successfully from our platform, we may not receive confirmation from the operator.
False Positives
In some cases, operators may return a positive Delivery Report even when the message did not actually reach the recipient’s device — for example, if the message was accepted by an intermediary system but failed at a later stage. These “false positives” can occur due to network congestion, temporary handset issues, or routing through aggregators that report success prematurely. As a result, a “delivered” status should not always be interpreted as definitive proof of successful receipt.
3. Content Filtering by Operators
Mobile operators may block or delay messages based on:
Links or shortened URLs
Specific keywords
Suspicious or high-risk content
Uncommon symbols or formatting
Filtering rules vary between countries and may change frequently without notice.
4. Encoding and Character Issues
Messages containing characters outside the GSM-7 alphabet—such as å, ä, ö, emojis, or Asian-language characters—may trigger Unicode (UCS-2) encoding. When this happens, the maximum message length becomes much shorter and may lead to:
Truncated text
Multipart (split) messages
Corrupted or missing characters
When a message becomes multipart, each segment is sent separately and must be reassembled by the recipient’s device. Because every segment must arrive correctly, multipart messages have a lower chance of being delivered successfully. Keeping messages short can therefore improve delivery reliability.
To explain how this works:
An SMS can be up to 160 characters if it uses GSM-7 encoding (standard Latin letters, numbers, and most common symbols).
An SMS can be up to 70 characters if it uses UCS-2 encoding (needed for special characters, emojis, or scripts such as Chinese, Arabic, Thai, etc.).
If the message exceeds these limits, it becomes a multipart SMS, where each part has even fewer usable characters (153 for GSM-7 and 67 for UCS-2 per segment).
Because multipart SMS depends on multiple successful transmissions, keeping messages concise and avoiding special characters where possible increases the likelihood of successful delivery.
5. Failover and Routing Challenges
If an operator route or SMS provider is temporarily unavailable, traffic must be rerouted. This fallback process (“failover”) is handled by SMS gateways, but these mechanisms are not always visible or detectable from our side. Combined with the lack of guaranteed delivery, this can result in undelivered messages.
6. Local Regulations and Compliance Rules
SMS compliance laws differ across markets. Some countries impose strict rules on:
Bulk or high-volume SMS
“Transactional” vs. “Promotional” message categories
Sender ID formats
Message timing and approved content
Non-compliant messages may be filtered or rejected by local operators.
7. Dependence on External SMS Providers
SMS delivery relies on third-party carriers and global gateway partners. A temporary outage or degradation at one provider can affect delivery to specific regions or networks. Even a single global gateway may act as a “single point of failure” in some scenarios.
If You Still Haven’t Received an SMS
If you or your users experience repeated issues, we recommend checking:
Correct phone number format, including country prefix
Device signal and roaming settings
Whether the device can receive other SMS from international numbers
Whether the number has previously opted out of similar messages
You are also welcome to contact our support team for further assistance.