Companies expanding into overseas markets often encounter issues like these:The backend shows that an SMS was sent successfully, yet the user never receives it; delivery rates suddenly drop in certain countries; verification code delays affect registration and login; marketing messages are quietly blocked, causing promotional budgets to be wasted.

These issues can stem from multiple factors. An international SMS must pass through several stages—from submission and delivery to the user’s mobile phone—including content review, routing, carrier networks, and terminal reception. An issue at any stage can affect the final delivery rate.

Today, drawing on ITNIO TECH’s years of hands-on experience in international communications for enterprises expanding overseas, Songliang will break down the key factors affecting SMS delivery rates and share seven practical optimization methods.


1. What Is the SMS Delivery Rate?

When it comes to SMS delivery, many people confuse “sent successfully” with “received by the user.”

In most cases, when a platform returns “submission successful” after an SMS is sent, this only means that the message has entered the delivery process. It does not mean that the user has received it. To determine whether the message was delivered, businesses need to combine carrier delivery receipts, failure reasons, verification-code completion rates, and other data for a comprehensive assessment.

SMS delivery rate formula:

Successful deliveries ÷ total submitted messages × 100%

SMS delivery rates can vary significantly across different business scenarios. Based on ITNIO TECH’s years of experience in international enterprise communications, we have summarized the following reference ranges for three typical scenarios.

2. How Can You Improve International SMS Delivery Rates?

2.1  Use Multiple Channels and Switch Automatically During Failures

Many overseas teams initially rely on a single SMS channel. Everything works smoothly while the channel is stable, but carrier maintenance, regional network congestion, or peak traffic during major promotions can suddenly lead to widespread delays or delivery failures—with no backup option available.

The key solution is multi-channel redundancy combined with intelligent routing.

For every message, the system automatically selects the optimal route based on factors such as the destination country, carrier, real-time latency, and cost. If a channel experiences timeouts, an increase in blocking rates, or other abnormalities, the system automatically switches to a backup channel to ensure uninterrupted delivery.

2.2 Apply for a Sender ID in Advance and Establish Local Delivery Channels

A Sender ID is the phone number or name displayed on the recipient’s device when an SMS is received.

Many countries require Sender IDs to be registered and approved in advance. If messages are sent without the required registration, carriers may quietly block them. Although the backend may still display “submission successful,” users may never receive the messages, and no error may be returned.

Requirements vary widely by country and carrier, including the rules for Sender ID registration. Before entering a new market, businesses can apply directly to local carriers in the target market.

However, a more efficient approach is to work with a service provider such as ITNIO TECH. We are familiar with carrier registration procedures and can provide end-to-end support, helping businesses avoid launch delays caused by repeatedly rejected application materials.

2.3 Optimize Message Content and Length to Reduce Blocking and Control Costs

Carriers around the world generally deploy anti-spam systems, so message content directly affects both delivery rates and costs.

First, consider encoding and message length. GSM-7 is the standard encoding for GSM messages and supports English, numbers, and certain punctuation marks. A single message can contain up to 160 characters. If the content includes Chinese characters, certain special symbols, or emojis, it may switch to UCS-2 encoding, reducing the capacity to 70 characters per segment. Once a message exceeds the single-segment limit, it is split into multiple segments, resulting in multiple charges and higher costs.

Second, use consistent templates for the same type of SMS whenever possible. This helps build a positive reputation with carriers and improves approval rates. Businesses are also advised to use branded short links under their own domains. These links are generally more trusted by carriers than public short-link services and are less likely to be filtered.

In addition, avoid using all-capital lettering, repeated exclamation marks, and highly promotional or manipulative language. Such content is easily identified by anti-spam systems, significantly increasing the risk of blocking.

2.4  Clean Your Number Database to Improve Delivery Accuracy

Many businesses’ customer databases contain invalid numbers, such as numbers that have been disconnected after a change of phone number, numbers entered incorrectly during registration, or numbers belonging to users who have already opted out of receiving messages. Sending SMS messages to these numbers not only wastes money but also damages the account’s reputation with carriers, potentially resulting in Sender ID suspension or extremely costly fines.

To prevent this, businesses should require users to enter phone numbers in an internationally standardized format during registration.

Businesses should also regularly remove numbers that repeatedly return failure messages such as “number does not exist” or “service suspended.” Numbers belonging to users who have explicitly opted out should be removed promptly as well.

2.5  Monitor and Review Data in Real Time to Identify Conversion Failures

Optimizing delivery rates is not a one-time task. It requires continuous monitoring of data changes.

Businesses should track SMS reports by country, carrier, and time period. They should also use business conversion data to determine whether a channel may be underperforming. For example, verification-code flows should be evaluated based on the “sent → successfully verified” rate, while marketing messages should be evaluated based on the “sent → clicked” rate. If delivery rates are high but conversions are abnormal, businesses should investigate potential channel-quality issues.

Before major promotional events, carrier networks are often congested. Businesses can send a small amount of test traffic to carriers several days in advance. Once they confirm that there are no abnormal blocks, they can scale up traffic officially and avoid discovering problems only on the day of the campaign.

2.6  Choose the Right Sending Time to Reduce Unsubscribes and Complaints

When using SMS to communicate with overseas customers, the timing and frequency of messages are also important.

First, schedule messages according to the recipient’s local time. User habits differ across time zones. Sending marketing messages late at night in the recipient’s local time not only produces poor conversion results but may also lead to more unsubscribes and complaints.

Second, control the sending frequency for each user. Repeatedly sending messages to the same user within a short period can easily be classified as abusive traffic and may also cause user dissatisfaction and complaints.

2.7  Use Multi-Channel Verification to Retain Users During Registration

In international communications, a single channel typically cannot guarantee 100% delivery of verification codes. Poor signal, roaming users, and channel rate limits can all cause delivery failures.

Businesses should therefore configure multi-channel user verification. For example, SMS verification codes can be used as the primary method, with voice verification as a backup. If the SMS is not delivered successfully within 60 seconds, the system can switch to voice verification.

In addition, during user registration and account login, businesses can add social messaging channels such as WhatsApp as a third layer of backup, improving registration and login success rates.

3. Common Issues with International SMS Communications

The final delivery rate of international SMS is affected by multiple factors, including channel quality, local compliance, number validity, sending time, and carrier network conditions.

For businesses expanding overseas, it is best to establish a complete delivery process: complete compliance preparations and small-scale testing before launch; use multi-channel routing and real-time monitoring to identify issues promptly during delivery; and continuously review performance after delivery based on delivery receipts and business data.

If your business is experiencing verification-code delays, declining delivery rates in certain countries, blocked SMS messages, or high delivery costs, ITNIO TECH can assess your existing delivery setup based on your target countries, business type, and message volume, and provide a customized international SMS optimization solution.

ITNIO TECH
Helping businesses expanding overseas connect seamlessly with users worldwide and ensuring efficient delivery of business SMS messages.


Global Coverage — Direct connections with more than 100 carriers, covering over 200 countries and regions
Intelligent Routing — Intelligent switching across multiple channels, with 24/7 channel-quality monitoring
Compliance Support — Assistance with Sender ID registration and local compliance guidance in multiple countries worldwide
Multi-Channel Verification — Multi-channel verification through SMS, voice, and WhatsApp
Transparent Data — Real-time reports by country and carrier, including detailed failure reasons
Fast Integration — Rapid API/SDK integration, providing access to SMS and voice capabilities through a single integration