Messaging deliverability FAQ


Rachel Vinogradov


What is spam? 

Spam refers to unwanted or unsolicited text messages received by a consumer. Bandwidth leverages industry-sanctioned and industry-sourced spam filtering technologies to stop all forms of spam from reaching the text messaging ecosystem. 

How does spam filtering work?

In keeping with the mobile network carriers' policies, Bandwidth is required to minimize the flow of spam into the messaging industry. The carriers require that every provider with a connection to their network(s) utilize some sort of spam filtering on their traffic.

Spam filtering exists for two reasons:

  1. To protect consumers from unwanted messages (spam, fraud, or abuse)
  2. Enforcement tool to regulate messages that violate Bandwidth and carrier policies

Many factors determine whether a message gets flagged by a spam filter. There's a built-in layer of machine learning that's being constantly updated based on sending patterns, sending volume, message content, end-user opt-outs, end-user complaints made to carriers associated with the content or sending number, and a variety of other factors. These updates happen faster than any human can comprehend based on what's being sent across the messaging ecosystem.

Note: Due to the proprietary nature of spam filter information and to prevent bad actors from evading our spam filters, Bandwidth may not always be able to provide specific details regarding what initiated a block.

How does message deliverability work?

Every message travels across an elaborate web of interconnected carrier networks encountering a number of checkpoints that carriers like Bandwidth use to check for spam. There are different levels of spam filtering (Bandwidth, downstream provider, carrier), all designed to protect consumers from unwanted text messages. Each level has its own set of spam rules that can inadvertently cause a message to be blocked.

A message being flagged by a spam filter is the trigger to notify parties that a human needs to review the content to confirm if the message(s) is either confirmed spam or a false positive. All messages sent through the messaging ecosystem are subject to blocking regardless of verification/registration status. A number being verified/registered doesn't mean it won't experience any blocking. It means these messages are subject to less spam filtering through our carrier's network. We understand message blocks are inconvenient, especially if it’s a false positive, but it's also a way of letting us know our filtering is working as designed.

Note: Bandwidth cannot whitelist messages or guarantee deliverability on a number.

How can I avoid spam filtering?

The best way to prevent your messages from being filtered is to avoid sending spam or fraudulent traffic and ensure that you're following the guidelines in Bandwidth's State of Messaging 2023, Bandwidth Messaging Content Policies, Acceptable Use Policy, and CTIA Messaging Principles and Best Practices.

Below we’ve listed the most important elements of a message that with the proper adherence can help minimize the chances of encountering a spam filter.


Consent can mean many things, but in this case, we’re talking about any written or verbal confirmation that the message recipient gives to the message sender before messages are sent. In the messaging world, this is often referred to as opt-in.

Please ensure you’re only sending wanted messages to consumers who have provided their consent. Opt-in lists should be regularly scrubbed to ensure only opted-in handsets are receiving messages. If anyone has requested to be removed from the sending list, it must be honored. Opt-in records should be stored and easily referenceable in case they're requested during a blocking event or audit.

Note: If you're unable to provide proof of opt-in consent, you risk having a number/campaign blocked until sufficient information has been provided to remedy the ask.


Message senders have obligations to process opt-outs so that the phone number is removed from all distribution lists and logged as “opted out” from SMS communications. This ensures that future messages are not attempted and consumer consent is honored.

Use case

Ensure the use case doesn't fall under prohibited content or campaign type.

Single number sending

Snowshoeing messages across multiple phone numbers, with the same or similar content, to evade spam filters is a disallowed practice. In most cases, a business should be associated with a single primary phone number.


Please see Messaging URL best practices.

Natural language

All messages should include natural language. You should avoid using non-standard spelling of words, and unnecessary special characters or capitalization of words.

My messages are being blocked. What should I do?

Message filtering enforces Bandwidth policies or the wireless carriers' messaging policies and may occur because the messages are unwanted. If you've reviewed your traffic and it complies with the above messaging policies, please open a ticket with our Messaging Deliverability team.

When opening a support ticket please provide the following information:

  • Source number
  • Destination number
  • Date/Timestamp
  • A sample message of blocked content
  • Campaign ID, if applicable

Failure to provide all necessary information may result in a longer turnaround time. With the above information provided, the Messaging Deliverability team will investigate and advocate with the appropriate aggregator for resolution. 

What are the standard spam block timelines?

4470 (Bandwidth) Resolution time is dependent on the type of internal filtering. Certain instances require higher clearance to unblock the content. These blocks generally take up to 24 business hours to resolve from the time the team engages our partner.
4750/4770 (Downstream)

Resolution times vary for blocking events outside of the Bandwidth network. Blocks can take up to 72 business hours to receive a first response from our messaging aggregator. The first response does not usually result in remediation. Our downstream partner may ask for additional details before lifting a block on a number.

If you haven't received an updated response from Bandwidth within 3 business days of an investigation being opened with our downstream provider, please update your ticket requesting to escalate. The team can then begin escalating for an update with our downstream partner

Note: Bandwidth doesn't support unregistered traffic. Our Messaging Deliverability team is not able to investigate downstream spam blocks that are sending unregistered or unverified traffic. 

If a TN is blocked from sending on an unregistered route, we are unable to remediate the TN, even if it is subsequently added to a campaign after the block originally occurred. These blocks can be in place for up to 30 days.

My campaign was vetted and approved. Why are my messages being blocked?

The Campaign Registry (TCR) allows businesses to register their 10DLC campaigns and store the campaign information (use case, brand name, opt-in information, etc) in a centralized location for the carriers. Campaign vetting and approval do not systematically remove or prevent spam blocking.

If the message traffic aligns with a properly registered campaign in TCR, it allows us to work more swiftly with our downstream partners to advocate for the remediation of the block(s). If content changes/differs from approved campaign purposes or if language is sent over the number that triggers a filter, the number may be blocked. For example, if cannabis traffic is sent on a number, it should create a block.

Can I escalate a blocking event?

Due to the heightened sensitivity of blocking events, all blocking events are treated with urgency. Downstream blocks require coordination and review from multiple parties. Since the block happened outside of the Bandwidth network, our capacity to lift the block is limited and we have to rely on our peer to remediate on our behalf. 

If you'd like to escalate a block, please update the support ticket with the request to escalate and the reason for it. We'll make all reasonable efforts to resolve blocking events in a timely fashion and adhere to the above guidelines from our vendors. Unfortunately, we can't guarantee that any party will be able to lift a block within a specific timeframe, but we'll do our best to resolve it as soon as possible and keep you updated every step of the way. 

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