Country-Specific Restrictions and Features

Carriers in the United Kingdom are now filtering Application-to-Person (A2P) SMS to protect consumers from spam, fraud, and bad actors. To ensure your messaging services remain uninterrupted, Plivo strongly recommends registering your sender IDs following Know Your Customer (KYC) guidelines to avoid having your messages either partially or completely blocked.

What do you need to do?

Sender IDs must comply with UK sender ID guidelines documented below. Additionally, ensure that your content templates and URLs are whitelisted.

Sender ID format

• International sender IDs are prohibited (such as non-local long codes and toll-free numbers).
• Numeric sender IDs starting with 6/7/8 are no longer allowed.
• Local numeric sender IDs must start with a 44 prefix and be registered by your brand. 
• Alphabetical sender IDs should indicate your brand and adhere to the character limits (0-9 and A-Z).
  
  

Note: Between the two sender ID options, Plivo recommends opting for Alphabetical sender IDs. This choice ensures better brand representation and, consequently, enhances message delivery.

Required documentation

To register a sender ID, submit the following on Plivo Console:

• Sender ID
• Company name
• Company website
• SMS template (submit multiple if numerous templates are in use)
• URL (if applicable)
• Messaging use case

Per regulatory guidelines, businesses operating within the financial sector—including mortgage companies, lenders, traders, and banking institutions—are required to submit a Letter of Authorization (LOA) to Plivo before registering their Sender IDs. To facilitate this process, such customers should contact our support team for assistance.

Guidelines for resellers

Who is considered a Reseller?

Businesses facilitating Application-to-Person (A2P) messaging for other businesses are regarded as resellers. 

Requirements for Resellers:

UK carrier regulations mandate the registration of sender IDs for customer-facing brands transmitting these messages. Resellers must furnish the requisite documentation of such brands through the Plivo console.

Important Note for Resellers:

Unique Sender IDs: Resellers are advised against utilizing a single sender ID for multiple brands, as this may result in partial or complete blocking of the sender ID. It is imperative for each individual brand to possess its distinct sender ID to ensure accurate identification and successful message delivery.

Timelines and Charges

Note that sender ID registration typically takes 15-20 working days. For customers in a contract with Plivo, there are no one-time or recurring costs associated with sender ID registration. However, customers not in a contract with Plivo may incur a $25 fee per sender ID.

Next steps

Log in to your Plivo account to begin the process. If you have any further questions or need assistance, please contact the Plivo Support team.

Sending messages to US destinations from Canadian long codes is not permitted. Plivo suggests using a US long code, toll-free number, or short code instead.

Under Singapore’s Full SMS Sender ID Registry (SSIR) Regime, all organizations that send SMS messages to Singapore mobile numbers must register their sender IDs with the Singapore Network Information Centre (SGNIC), the national registry responsible for authorizing and regulating sender ID registration. Registration is required for alpha and alphanumeric sender IDs, dedicated short codes, and dedicated virtual long numbers. 

Post July 31, 2023, Singapore operators will pass through only messages with registered sender IDs. Messages from unregistered sender will be passed  as “possible spam” for the interim (pending SG-NIC update)

To comply with the requirements and avoid any disruption to their SMS communications, businesses must register their accounts and submit their preferred sender ID(s) via the SSIR portal and assign Participating Aggregators (PA). 

How to create an account

To register your sender IDs you must first create an account on the SSIR portal. 

Only organizations with a local unique entity number (UEN) as issued by relevant government agencies can register with the SSIR. If you don’t have a UEN but want to obtain one, follow these instructions. 

Foreign-based businesses can obtain a UEN by registering with the Accounting and Corporate Regulatory Authority (ACRA). Foreign-based businesses can register for sender IDs with SSIR via their local subsidiary or foreign branch office as long as the local subsidiary or foreign branch office can present a valid UEN. Non-business organizations (such as charities or religious bodies) can register with agencies that issue UENs to these types of organizations. 

Currently there doesn’t seem to be a way for businesses without a UEN to register on the SSIR portal. . Please let your customer success manager or our support team know if you’re unable to obtain a Singapore UEN. 

Once you have a UEN, register your account on the SSIR portal. SGNIC will notify you when your account has been approved. The process takes about two days.

How to register sender IDs

Once you have an account you can submit the sender ID(s) you’d like to send messages from. Review the rules for valid sender IDs, then enter your information in the SSIR Portal.

During registration you’ll be asked to choose one or more Participating Aggregators (PA). Choose these PAs to ensure Plivo can successfully terminate your Singapore messages.

• MACRO KIOSK PTE LTD
• HELLO TECHNOLOGY PTE LTD
• MOCEAN PTE LTD
• GREEN PACKET GLOBAL PTE LTD

The process of getting SSIR approval for sender ID registration takes about a week.

How to add PAs if you already have a registered sender ID

If you’ve already registered sender IDs and you need to add PAs, you must send an email message to SGNIC, cc-ing Plivo, asking them to add the aforementioned PAs to the the list of those authorized for your sender ID. Here’s an example email.

Create a Letter of Authorization

Once your registration is approved, create a Letter of Authorization (LOA) [template] and submit it to Plivo as an attachment to a support ticket. We need the LOA so we can inform the Singapore authorities that you’re allowing Plivo to send messages using your sender IDs. Once we receive your signed LOA, we will get your sender IDs whitelisted with Singapore operators. This process can take up to two days. Once it’s complete you can start sending messages to Singapore mobile subscribers.

Pricing

SSIR bills organizations for setup fees and sender IDs; an invoice will be emailed to the organization’s designated billing contact.

These fees are payable to SGNIC (Singapore Network Information Centre).

When you send an SMS message to a US or Canada destination number, use a US long code number from your Plivo account in the international format. If you use any other number in the source parameter, you'll get the error "this caller ID is not allowed for outbound message."

Long codes are traditional 10-digit phone numbers used for both voice calls and SMS in the U.S. and Canada. With the introduction of 10DLC (10-Digit Long Code) in the United States, local long codes can now be used for Application-to-Person (A2P) messaging, provided they are properly registered, follow carrier guidelines, and comply with messaging regulations. However, carriers will still block messages under certain circumstances.

Common Reasons for SMS Blocking
Carriers may block SMS messages if they detect patterns or content that violate their policies or industry guidelines. Some common reasons include:

• Non-Compliance with 10DLC Registration and Guidelines:
  Messages sent from unregistered or improperly configured 10DLC numbers may be blocked. Ensure that your A2P campaign is registered and complies with carrier rules.
• Excessive Sending Rates Without Proper Registration:
  Sending a high volume of messages too quickly from a long code without adhering to your assigned 10DLC throughput may trigger blocking.
• Imbalanced Incoming-to-Outgoing Ratios:
  If the ratio of incoming messages to outgoing messages on your long code exceeds acceptable thresholds (for example, a ratio higher than 1:3), carriers may flag and block your messages.
• Repeated or Rapid-Fire Messaging:
  Sending the same message multiple times to the same user within a few seconds can appear as spam and lead to blocking.
• Use of Prohibited Content:
  Messages containing disallowed content—such as illegal offers, hate speech, phishing attempts, or other violations of carrier guidelines—will be blocked.
• Problematic Links and Keywords:
  Messages that contain suspicious URLs, repetitive keywords, or link shorteners may raise spam flags and result in blocking.
• Multi-Unit (Multipart) Messages:
  While allowed, longer messages split into multiple segments (multipart messages) may sometimes be scrutinized, increasing the risk of blocking if they resemble spam.

Note: When sending SMS to US destination numbers, specify your US Plivo long code number in E.164 format. If you don't, you'll get the error message "This caller ID is not allowed for outbound message.

We provide an application-level flag to control whether message content or source numbers from incoming messages to Plivo phone numbers should be redacted from Plivo debug logs and databases.

When message redaction is enabled for an application, we make three kinds of redactions:

1. The content of incoming messages to Plivo phone numbers associated with the application are redacted from all internal Plivo server logs and the debug logs available on the Plivo console.
2. The last three digits of the source number from which the SMS originated are redacted from all internal Plivo server logs and the debug logs available on the Plivo console.
3. The last three digits of the source number from which the SMS originated are redacted from the Message Detail Record (MDR) generated for the message. Fetching MDRs for such messages would then return the redacted source numbers.

Configuring message redaction for Plivo applications

Message redaction is disabled by default. You can enable and disable it through the Plivo console or by using the application XML object.

Turning message redaction on or off from the Plivo console

Visit Messaging > XML Applications and select the application you're interested in. Toggle the Redact Incoming Messages checkbox to enable and disable redaction for incoming messages to phone numbers associated with the application.

Turning message redaction on or off using the Application XML object

Use the log_incoming_messages attribute of the application resource to enable or disable message redaction.

When creating a new application, set the log_incoming_messages attribute to false in the Create Application API request to enable message redaction. The default value for this attribute is true, which means that message redaction is disabled.

You can enable or disable message redaction for any application at any time using the Update Application API.

How does message redaction impact the message URL payload?

Message redaction offer you control over message details that may be logged in Plivo systems for debugging purposes.

If a message_url has been configured, Plivo will attempt to post the nonredacted message content and the nonredacted source number to it.

For enhanced security, we recommend that you configure secure HTTPS endpoints for message URLs.

Plivo can identify invalid and non-SMS-enabled destination numbers. Since we don’t accept delivery messages sent to invalid destination numbers, we do not charge for them. We can also fix incorrectly formatted destination numbers to improve delivery rates and provide a better end-user experience. 

Synchronous handling for invalid numbers

Customers can propagate an invalidation error upstream easily since SMS API requests to invalid and non-SMS-enabled numbers are rejected with a 400 Bad Request API response. Here’s an example of how this works in a one-time password (OTP) use case:

Step 1: A user requests an OTP on an invalid destination number.

Step 2: The customer initiates a Send SMS API request.

Step 3: Plivo returns 400 Bad Request response synchronously.

Step 4: The customer displays an "invalid number" error to the user. 

Format correction for phone numbers

Plivo can intelligently reformat incorrectly formatted phone numbers. Here are two scenarios to illustrate how this works. 

Scenario 1: A user enters the Lithuanian number 370860112345. Plivo automatically reformats the number to the E.164 international format +37060112345 before forwarding the message to downstream carriers. Notice the 8 has been removed in the formatted number. This is because Plivo recognizes that 8 is required only when dialing a Lithuanian number from inside Lithuania.

Scenario 2: A user enters the Mexico number 520455512345678. Plivo automatically reformats the number to E.164 international format +5215512345678. Notice that 045 has been replaced with 1. This is because 045 is only to be used when dialing a domestic cell phone from a landline, and 521 is the prefix for mobile phone numbers in E.164 format.

Enabling Enhanced Destination Number Validation

•   All new Plivo customers have Enhanced Destination Number Validation for SMS enabled by default.
•   Existing customers can enable Enhanced Destination Number Validation for SMS from the SMS Settings page of the Plivo console. We recommend that all of our customers enable this feature.

Note: Because landlines in the US, Canada, and the UK can be enabled for SMS, Plivo will not reject SMS messages to landline numbers in these countries.

A2P (application-to-person) and P2P (person-to-person) are two distinct categories of SMS messaging. Determining which approach to use depends on the type of traffic you’re sending, the volume of messages, and regional regulations.

• A2P (Application-to-Person):
  Messages originate from an application rather than an individual. A2P messaging is designed for higher volumes and is often used for things like marketing campaigns, appointment reminders, and alerts.
• P2P (Person-to-Person):
  Messages are sent by individuals to individuals. P2P messaging involves lower volumes and should mirror natural human conversation. Typically, P2P traffic should not exceed one message per second per number and should be truly conversational.

P2P and A2P Messaging in the US and Canada
The United States and Canada both regulate SMS traffic.

• In the US, A2P messaging is supported via 10DLC (10-digit long codes) specifically intended for application-based use cases. This ensures that A2P traffic is routed through approved channels that meet regulatory and carrier guidelines.
• In Canada, long codes should be used primarily for P2P (two-way) conversational messaging. P2P messaging in Canada should closely resemble human-like interactions in both volume and frequency.

Carriers in both countries use spam filters to identify and block non-compliant traffic. If you have questions about sending A2P or P2P messages, please contact us for guidance on compliant practices.

International Destinations
Plivo partners with major international telecom operators (directly or through trusted intermediaries) to support sanctioned A2P traffic globally. However, rules vary by country. Some regions impose restrictions on message content, volume, and frequency. For details on country-specific regulations, please reach out to your account executive.

Many of our clients need to send messages in bulk to customers and prospects. SMS bulk messaging has been the subject to scrutiny in recent times because it can be used to send spam messages. Operators and regulatory bodies are sensitive to the number of messages that can be sent per minute from a given number. Limiting send rates, however, can have negative business impact in the form of reduced customer reach.

Plivo’s messaging platform solves this problem by delivering messages to downstream operators using smart queuing based on the type of source number used and the destination country. We maintain a dedicated queue for each of your source numbers. If you need to send messages using the Plivo SMS API to a specific destination country at a throughput greater than what's available from a single source number, you can increase your overall capacity by distributing your traffic across a pool of Plivo numbers to get the throughput you need while staying within the recommended per-number rate limits.

Do I need to contact you to get this feature enabled on my Plivo account?

No — smart queuing is enabled for Plivo accounts by default.

How do I determine the status of a message? Can I see whether it's queued or has been sent out?

When a message is in the queue, its status is set to "queued." The message is marked as "sent" once it has been passed on to downstream carrier networks. For more information about message statuses, visit our Message Object API reference documentation.

Are these the only rate limits that apply to my SMS traffic?

You can send SMS requests to Plivo at any rate you wish. All messages are put into the primary queue and dequeued based on the account-level messages per second rate configured for your account. Messages are then throttled for final delivery by our smart queue based on the source type and destination country.

Will the smart queue process messages in the order in which they were sent to Plivo?

Yes, messages are never processed out of order.

How are long (multipart) messages handled?

Multipart messages are enqueued, dequeued, and processed as a single entity at all times. The dequeue rate of a message is autoadjusted based on the size of the message to ensure that your traffic remains compliant regardless of the size of the message. For instance, if you send a two-part SMS message from a US source number, the message would be dequeued two seconds after the previous message in that source number’s queue.