How to Send SMS in Japan: Complete Compliance & Integration Guide

Sending SMS in Japan requires understanding strict regulatory requirements and technical specifications across four major carriers. This guide covers everything you need to send SMS messages to Japanese customers compliantly in 2024, including regulatory compliance with Japan's Anti-Spam Act and APPI, carrier-specific technical requirements for NTT DOCOMO, KDDI, SoftBank, and Rakuten Mobile, and API integration with Twilio, Sinch, MessageBird, and Plivo.

Market Overview

Market Landscape: Japan's mobile market is dominated by four major carriers: NTT DOCOMO (holding the highest market share in 2024), KDDI (au), SoftBank, and Rakuten Mobile (launched as a full mobile network operator in 2020, surpassing 8 million subscribers by October 2024). While OTT messaging apps like LINE dominate personal communications, SMS remains essential for business use – authentication, notifications, and customer service. The market strongly prefers iOS devices, though Android maintains significant presence. Expect high delivery rates due to robust infrastructure and strict regulatory compliance.

Key SMS Features and Capabilities in Japan

Japan supports comprehensive SMS capabilities including two-way messaging, concatenation, and strict regulatory compliance across all major carriers.

Two-Way SMS Support

Status: Fully supported

Two-way SMS enables interactive messaging scenarios like customer service, appointment confirmations, and automated responses. No special restrictions apply beyond standard compliance requirements.

Concatenated Messages (Segmented SMS)

Support: Yes, across all major Japanese carriers (support may vary by sender ID type)

Message Length Rules:

• Standard: 160 characters per segment (GSM-7 encoding)
• Japanese text: 70 characters per segment (UCS-2 encoding for Kanji, Hiragana, Katakana)
• Messages exceeding limits are automatically concatenated

Carrier-Specific Limits:

• KDDI (au): Maximum 5 segments per message (140 characters with default character set, 70 with special characters)
• SoftBank: Up to 664 characters with default character set, 332 with special characters
• NTT DOCOMO/Rakuten: Up to 660 characters

Encoding: Both GSM-7 and UCS-2 supported

MMS Support

Status: Not available through standard SMS channels

Convert MMS content to SMS with URL links. Use short URLs and clearly indicate when links lead to media content.

Recipient Phone Number Compatibility

Number Portability

Status: Fully available across all major carriers

Users can keep their phone numbers when switching providers. Always use +81 format for reliable delivery.

Can You Send SMS to Landlines in Japan?

Status: Not supported

Attempts to send SMS to landline numbers will fail with a 400 response error (code 21614). Messages won't appear in logs, and you won't be charged for failed attempts.

What Are Japan's SMS Compliance and Regulatory Requirements?

SMS communications in Japan are regulated by the Ministry of Internal Affairs and Communications (MIC) and the Personal Information Protection Commission (PPC). You must comply with the Act on Regulation of Transmission of Specific Electronic Mail (Anti-Spam Act), the Act on the Protection of Personal Information (APPI, effective with April 2024 amendments), and the Act on Specified Commercial Transactions (ASCT). These regulations govern how you collect, use, and protect personal information, including phone numbers.

Critical Restriction: URLs in SMS messages are strictly prohibited or heavily filtered by Japanese carriers. Any message with a weblink may be blocked entirely.

2024 Update: Under APPI amendments effective April 2024, you must report actual or suspected leakage of personal information before database incorporation due to malicious acts.

How to Get Consent for SMS Marketing in Japan

Explicit Consent Requirements:

• Obtain written or digital consent before sending any marketing messages (opt-in system required under Anti-Spam Act and ASCT)
• Recipients must explicitly consent to receive marketing messages; you cannot send unsolicited commercial SMS
• Maintain consent records and make them easily accessible
• Clearly state the purpose of communication during opt-in
• Use double opt-in for marketing messages (strongly recommended)

Documentation Best Practices:

• Store timestamp and source of consent
• Maintain detailed records of opt-in method and context
• Keep consent records for at least 2 years
• Conduct regular audits of consent database

HELP/STOP and Other Commands

Required Features:

• Include opt-out instructions in Japanese in all messages
• Support standard keywords in both English and Japanese:
  • STOP (停止)
  • HELP (ヘルプ)
  • CANCEL (取消)
• Provide immediate responses to HELP/STOP in Japanese

Do Not Call / Do Not Disturb Registries

Status: Japan does not maintain a centralized Do Not Call registry similar to those in other countries like the United States.

Requirements:

• Maintain internal suppression lists for opt-outs
• Honor opt-out requests within 24 hours
• Conduct regular database cleaning to remove inactive numbers
• Comply with the Act on Specified Commercial Transactions for telemarketing regulations

What Are the Best Times to Send SMS in Japan?

Sending Hours:

• Restricted to 9:00 AM – 8:00 PM JST (Japan Standard Time)
• Emergency messages exempt from time restrictions
• Avoid sending on national holidays and weekends (recommended)
• Consider regional time differences for international businesses

What Sender ID Options Are Available in Japan?

Alphanumeric Sender ID

Operator Network Capability: Supported

Registration Requirements (2024):

• No pre-registration required with carriers – Japan supports dynamic alphanumeric sender IDs
• Sender IDs can be used instantly without carrier registration or associated fees
• Account must be enabled for alphanumeric sender IDs by your SMS provider (not enabled by default)

Sender ID Preservation:

• Dynamic sender IDs preserved when sent through international gateways
• Alphanumeric sender IDs are one-way only (recipients cannot reply)

Character Limits: 3–11 characters (letters, numbers, limited special characters)

Long Codes

Support:

• Domestic: Not supported
• International: Fully supported

Sender ID Preservation: Yes, for international long codes

Provisioning Time: Immediate for international numbers

Use Cases:

• Two-way communication
• Customer service
• Transactional messages

Short Codes

Support: Available through domestic gateway only

Provisioning Time: 5–8 weeks for approval

Use Cases:

• High-volume marketing campaigns
• Two-factor authentication
• Customer loyalty programs

What Content Is Restricted for SMS in Japan?

Prohibited Content:

• Firearms and weapons
• Gambling and betting
• Adult content
• Money lending/loan services
• Lead generation
• Political messages
• Religious content
• Controlled substances
• Cannabis products
• Alcohol-related content

Additional Restrictions:

• URLs are strictly prohibited or heavily filtered – messages with weblinks may be blocked entirely
• Phone numbers in message content not allowed
• M2M messaging supported on best-effort basis only

How Japanese Carriers Filter SMS Content

Carrier Filtering Rules:

• URLs from unapproved domains will be blocked
• No excessive punctuation or special characters
• Message length restrictions vary by carrier
• KDDI limits messages to 5 segments maximum

Tips to Avoid Blocking:

• Avoid including URLs (critical in Japan)
• Avoid spam trigger words
• Maintain consistent sending patterns
• Include clear company identification

Best Practices for Sending SMS in Japan

Messaging Strategy

• Keep messages under 70 characters when using Japanese text
• Include clear call-to-action
• Maintain consistent sender ID
• Use polite, formal Japanese language style (keigo)

Sending Frequency and Timing

• Limit to 1–2 messages per day per recipient
• Respect Japanese holidays and observances
• Avoid sending during early morning or late evening
• Space out bulk sends to prevent network congestion

Localization for Japanese Audiences

• Default to Japanese language unless recipient specifies otherwise
• Use proper honorifics and formal business Japanese (keigo)
• Consider cultural context and sensitivities
• Support both Japanese and English response handling

Opt-Out Management

• Process opt-outs within 24 hours
• Maintain centralized opt-out database
• Confirm opt-out with one final message
• Conduct regular cleanup of contact lists

Testing and Monitoring

• Test across all major carriers (NTT DOCOMO, KDDI, SoftBank, Rakuten Mobile)
• Monitor delivery rates by carrier
• Track opt-out rates and patterns
• Regularly test HELP/STOP functionality

How to Integrate SMS APIs for Japan

Twilio SMS Integration for Japan

Twilio provides robust SMS capabilities for Japan through their REST API. Authenticate using account SID and auth token credentials.

Key Parameters:

• to: Japanese phone numbers in E.164 format (+81XXXXXXXXXX)
• from: Your Twilio phone number or approved sender ID
• body: Message content (supports Unicode for Japanese characters)

import * as twilio from 'twilio';

// Initialize Twilio client
const client = twilio(
  process.env.TWILIO_ACCOUNT_SID,
  process.env.TWILIO_AUTH_TOKEN
);

async function sendJapaneseSMS() {
  try {
    const message = await client.messages.create({
      body: 'ご注文が完了しました。ありがとうございます。',
      from: process.env.TWILIO_PHONE_NUMBER,
      to: '+81XXXXXXXXXX'
    });
    
    console.log(`Message sent successfully: ${message.sid}`);
  } catch (error) {
    console.error('Error sending message:', error);
  }
}

Sinch SMS Integration for Japan

Sinch offers direct carrier connections in Japan with support for both Latin and Japanese character sets.

import { SinchClient } from '@sinch/sdk-core';

// Initialize Sinch client
const sinchClient = new SinchClient({
  projectId: process.env.SINCH_PROJECT_ID,
  keyId: process.env.SINCH_KEY_ID,
  keySecret: process.env.SINCH_KEY_SECRET
});

async function sendSMS() {
  try {
    const response = await sinchClient.sms.batches.send({
      sendSMSRequestBody: {
        to: ['+81XXXXXXXXXX'],
        from: 'YourCompany',
        body: 'ご確認ください。',
        encoding: 'UCS2' // Required for Japanese characters
      }
    });
    
    console.log('Message sent:', response.id);
  } catch (error) {
    console.error('Failed to send message:', error);
  }
}

MessageBird SMS Integration for Japan

MessageBird provides high-quality routes to Japanese carriers with Unicode message support.

import { MessageBird } from 'messagebird';

// Initialize MessageBird client
const messagebird = new MessageBird(process.env.MESSAGEBIRD_API_KEY);

// Configure message parameters
const params = {
  originator: 'COMPANY',
  recipients: ['+81XXXXXXXXXX'],
  body: '認証コード: 123456',
  type: 'unicode' // Enable Japanese character support
};

// Send message
messagebird.messages.create(params, (err, response) => {
  if (err) {
    console.error('Error:', err);
    return;
  }
  console.log('Message sent:', response.id);
});

Plivo SMS Integration for Japan

Plivo offers direct connectivity to Japanese carriers with support for long codes and alphanumeric sender IDs.

import plivo from 'plivo';

// Initialize Plivo client
const client = new plivo.Client(
  process.env.PLIVO_AUTH_ID,
  process.env.PLIVO_AUTH_TOKEN
);

async function sendPlivoSMS() {
  try {
    const response = await client.messages.create({
      src: 'COMPANY',
      dst: '+81XXXXXXXXXX',
      text: 'お支払い完了しました。',
      url_strip_query_params: false // Preserve URL parameters if included
    });
    
    console.log('Message sent with UUID:', response.messageUuid);
  } catch (error) {
    console.error('Failed to send message:', error);
  }
}

API Rate Limits and Throughput

Rate Limits:

• KDDI: 5 segments maximum per message
• General carrier limits: 30 messages per second
• Daily volume limits vary by provider and sender type

Throughput Management:

• Implement exponential backoff for retries
• Use queuing systems (Redis, RabbitMQ) for high volume
• Batch messages when possible
• Monitor delivery receipts for rate adjustments

Error Handling and Reporting

• Implement comprehensive logging with correlation IDs
• Monitor delivery receipts (DLRs) for status tracking
• Set up alerts for unusual error rates
• Store message metadata for troubleshooting
• Conduct regular audits of delivery performance by carrier

Frequently Asked Questions About SMS in Japan

Do I need to register my sender ID in Japan?

No, Japan supports dynamic alphanumeric sender IDs that require no pre-registration with carriers. However, your SMS provider account must be enabled for alphanumeric sender IDs (not enabled by default). You can use sender IDs instantly without registration fees or carrier approval processes.

Can I include URLs in SMS messages to Japan?

URLs in SMS messages are strictly prohibited or heavily filtered by Japanese carriers. Messages containing weblinks will likely be blocked entirely. Avoid including any URLs in your SMS content when sending to Japan.

What laws govern SMS marketing in Japan?

SMS marketing in Japan is governed by three primary regulations: the Act on Regulation of Transmission of Specific Electronic Mail (Anti-Spam Act), which requires opt-in consent for marketing messages; the Act on the Protection of Personal Information (APPI), effective with April 2024 amendments; and the Act on Specified Commercial Transactions (ASCT). All three laws enforce strict opt-in requirements before sending commercial SMS.

What character encoding should I use for Japanese SMS?

Use UCS-2 encoding for Japanese characters (Kanji, Hiragana, Katakana), which limits messages to 70 characters per segment. GSM-7 encoding supports 160 characters per segment but only works for standard Latin characters. Most SMS APIs automatically detect and apply the correct encoding.

What are the SMS sending hour restrictions in Japan?

SMS messages in Japan should only be sent between 9:00 AM and 8:00 PM JST (Japan Standard Time). Emergency messages are exempt from these time restrictions. Additionally, it's recommended to avoid sending messages on national holidays and weekends.

Which mobile carriers operate in Japan?

Japan has four major mobile carriers: NTT DOCOMO (market leader), KDDI (operating under the "au" brand), SoftBank, and Rakuten Mobile (which surpassed 8 million subscribers in October 2024). All carriers support number portability, allowing users to keep their phone numbers when switching providers.

How long does it take to provision SMS services in Japan?

Provisioning time varies by sender type. International long codes are available immediately, alphanumeric sender IDs require no registration and are available instantly (once your provider account is enabled), and domestic short codes require 5–8 weeks for carrier approval. Most businesses can start sending SMS to Japan within 24 hours using international routes.

Summary and Additional Resources

Key Takeaways:

1. Obtain explicit opt-in consent before sending any marketing SMS (required by Anti-Spam Act and ASCT)
2. Never include URLs in messages – they are strictly prohibited or filtered by Japanese carriers
3. Respect sending hours: 9:00 AM – 8:00 PM JST only
4. Use UCS-2 encoding for Japanese characters (70 characters per segment)
5. No sender ID registration required – Japan supports dynamic alphanumeric sender IDs
6. Test across all four major carriers: NTT DOCOMO, KDDI, SoftBank, and Rakuten Mobile

Next Steps:

1. Review MIC and APPI guidelines for SMS communications
2. Implement compliant consent management systems with timestamp tracking
3. Set up monitoring and reporting infrastructure for all four carriers
4. Test message delivery across NTT DOCOMO, KDDI, SoftBank, and Rakuten Mobile
5. Configure proper UCS-2 encoding support in your SMS API integration

Official Regulatory Resources:

• Ministry of Internal Affairs and Communications (MIC)
• Personal Information Protection Commission
• Act on Protection of Personal Information (APPI) – English Translation
• Act on Specified Commercial Transactions – English Translation
• Telecommunications Business Act Guidelines

Carrier Documentation:

• KDDI Business SMS Guidelines
• NTT DOCOMO Enterprise Messaging Documentation
• SoftBank Corporate Messaging Standards
• Rakuten Mobile Developer Resources