SMS campaigns can be flagged as spam when messages violate carrier filtering rules, lack proper opt-in consent, or include suspicious content or formatting. Understanding carrier best practices — such as using clear opt-in/opt-out language, limiting promotional content, respecting volume limits, and following A2P registration requirements — helps keep messages deliverable and reduces the chance your traffic will be filtered or blocked. This guide breaks down common triggers and practical steps to optimize SMS campaigns for higher deliverability.
Your SMS Campaign Was Flagged as Spam. Here’s Why and What to Do Next.
Getting an SMS campaign flagged as spam is frustrating, especially when you’re confident you followed the rules. Messages stop delivering, response rates drop, and suddenly you’re debugging carrier behavior instead of building features.
The good news is that SMS filtering is rarely random. Most campaigns are flagged for a small set of predictable reasons tied to consent, content, and sending behavior. Once you understand what carriers look for, you can usually correct the issue without starting over.
This guide explains why SMS campaigns get flagged, what signals carriers evaluate, and how to adjust your messaging practices to restore deliverability.
Why SMS campaigns get flagged as spam
Carriers operate aggressive filtering systems to protect subscribers from unwanted messages. These systems evaluate traffic patterns, message content, sender identity, and recipient behavior.
Your campaign may be flagged if carriers detect signs that resemble unsolicited or deceptive messaging, even if that was not your intent.
Common red flags include:
Messages sent without clear opt-in
High-volume traffic from new or untrusted numbers
Promotional language that resembles known spam patterns
Missing or unclear opt-out instructions
Unregistered Application-to-Person (A2P) traffic
Filtering decisions are automated and probabilistic. A campaign does not need to violate every rule to be flagged, only enough of them at once.
SPAM may include (but is not limited to):
- Unsolicited bulk commercial messages
- "Phishing” messages intended to access private or confidential information via deception
- Other forms of abusive, harmful, malicious, unlawful, or otherwise inappropriate messages
- Messages that require an opt-in but did not obtain opt-in consent (or opt-in consent was revoked)
- Any unwanted SMS messages
Notice that last point: SPAM can be as simple as “unwanted messages.”
Lack of clear opt-in is the most common cause
Consent is the foundation of SMS deliverability.
If recipients did not explicitly agree to receive messages from your application, carriers are likely to treat the traffic as spam. This includes cases where opt-in language was implied, buried in terms of service, or collected indirectly.
Best practices for opt-in include:
Clear disclosure of message purpose
Explicit agreement from the recipient
Documentation of how and when consent was collected
If carriers cannot infer legitimate consent from your traffic patterns, filtering is likely.
Even if you gathered written opt-in consent, if there ever comes a point in time where a recipient has had enough, the recipient can opt-out at any time by sending “STOP”. Often you will see that if a carrier receives a high amount of opt-out messages, your content may start being actively flagged as SPAM by default.
At SignalWire, we will receive reports from our downstream providers if people are reporting your messages as SPAM. When we receive downstream SPAM reports, we must open an investigation into your traffic.
We will work with you to validate your current campaign and take steps to make sure your SMS/MMS content is compliant, and that your processes (including opt-ins and opt-outs) are up-to-date with the current requirements.
If we continue to see SPAM complaints on your SMS traffic, SignalWire may shut down your entire campaign.
There is no appeal process for this. Once a campaign is deactivated, we will not be able to allow the offending content on our platform. This is why it’s extremely important to us that you follow our messaging best practices to the best of your ability.
Message content can trigger filtering
Carrier systems analyze message text for patterns associated with abuse.
Common content-related triggers include:
Excessive use of promotional language
Shortened links with no domain reputation
Repetitive or templated messages sent at scale
Urgency-based phrasing that resembles phishing or scams
Even legitimate businesses can be caught by these filters if messages are too generic or resemble known spam campaigns.
Clarity and specificity matter. Messages that clearly identify the sender and purpose tend to perform better.
Sending behavior matters as much as content
How messages are sent is often as important as what they say.
Campaigns are more likely to be flagged when:
Large volumes are sent suddenly from a new number
Message traffic spikes without a warm-up period
Identical messages are sent to large lists simultaneously
Error rates or user opt-outs spike quickly
Gradual ramp-up and predictable sending patterns help establish trust with carriers.
Why A2P registration affects deliverability
In many regions, high-volume SMS traffic is classified as Application-to-Person (A2P) messaging and must be registered with carriers.
A2P registration provides carriers with:
Information about your use case
Expected message volume
Sample content
Brand identity and sender purpose
Unregistered A2P traffic is more likely to be filtered, even if the messages themselves are compliant.
If your campaign sends messages programmatically or at scale, registration is not optional.
How to recover a flagged SMS campaign
If your campaign has already been flagged, recovery usually involves correcting underlying signals rather than changing platforms.
Steps that often help restore deliverability include:
Reviewing and tightening opt-in language
Reducing send volume temporarily
Updating message templates to be more explicit
Ensuring opt-out instructions are present and functional
Completing or updating A2P registration details
Recovery is not always instant. Carriers need to observe improved behavior over time before restoring trust.
Preventing future spam flags
The most reliable way to avoid filtering issues is to design SMS workflows with carrier expectations in mind.
That means:
Treating SMS as a consent-driven channel
Sending fewer, more relevant messages
Using stable, identifiable sender numbers
Monitoring delivery and opt-out metrics continuously
SMS works best when messages are expected, helpful, and clearly tied to an action the recipient took.
Best practices to keep SMS campaigns active
Make sure you have opt-in consent
Opt-in consent is one of the most important things to consider if your content is receiving SPAM reports. Opt-in consent can help us prove to the carriers that the traffic was wanted, but when people start opting out, the carriers grow concerned.
A high opt-out ratio means the message content is no longer wanted by the recipient, justifying the carriers’ choice to start throttling or blocking.
Most A2P campaign use cases require express written consent to satisfy opt-in requirements. If the content of a campaign is P2P in nature (see proxy services for inmates or apps that offer a proxy number for conversational messaging) implied consent is acceptable.
Here are some use cases that always require express written consent:
2FA/One-Time Passwords
Account Notifications
Customer Care
Delivery Notifications
Fraud Alert Messaging
Educational
Marketing Messages
Polling and voting
Public Service Announcement
Security Alert
Political
Social
Sweepstakes
When it comes to opt-in consent, here are some things to keep in mind:
It needs to be clear what message recipients are subscribing to when they opt-in
Messages should only be sent after the end user has opted-in
Opt-in only applies to the individual campaign and can not be applied to other campaigns
Opt-in consent is non-transferable and non-assignable
Message Senders should not use opt-in lists that have been rented, sold, or shared to send messages
Message Senders should create and vet their own opt-in lists
Message Senders should retain and maintain all opt-in and opt-out requests in their records to ensure that future messages are not attempted (in the case of an opt-out request!) and consumer consent is honored to minimize SPAM.
Message Senders should process telephone deactivation files regularly (e.g., daily) and remove any deactivated telephone numbers from any opt-in lists
Depending on the use case, opt-in consent can be obtained in the following ways:
Entering a telephone number through a website
Clicking a button on a mobile webpage
Sending a message from the Consumer’s mobile device that contains an advertising keyword
Initiating the text message exchange in which the Message Sender replies to the Consumer only with responsive information
Signing up at a point-of-sale (POS) or other Message Sender on-site location
Opting-in over the phone using interactive voice response (IVR) technology
Message senders should also document opt-in consent by retaining the following data where applicable:
Timestamp of consent acquisition
Consent acquisition medium (e.g., cell-submit form, physical sign-up form, SMS keyword, etc.)
Capture of experience (e.g., language and action) used to secure consent
Specific campaign for which the opt-in was provided
IP address used to grant consent
Consumer phone number for which consent to receive messaging was granted
Identity of the individual who consented (name of the individual or other identifier (e.g., online user name, session ID, etc.))
Focus on maintaining high content quality
Ideally, you want to include identifying information in the first message you send to your newly opted-in recipients. You also want to include opt-out language.
An example of the picture perfect message format is as follows:
[Brand Name] [Message] [Opt-out Language]
For example, here is how a message would look from a SignalWire test campaign:
[SignalWire] This is a test message from SignalWire! Reply STOP to Opt Out.
A lack of identifying information may confuse message recipients and make them think they’re getting messages that they don’t want. This can be easily avoided with simple messaging branding or watermarks.
You also want to avoid typos, poor grammar, and limit unnecessary punctuation or emojis. If your content is coming from a business and looks messy or unprofessional, the recipients will likely see your messages as SPAM and treat them accordingly.
Links can be an issue as well, especially if they don’t lead back to a legitimate website that includes branding, contact information, a privacy policy and terms and conditions pages.
Our carriers do not like seeing public URL shorteners being used. Avoid at all costs!
Clarify your messaging frequency upfront
When message recipients opt-in, they need to be informed how frequently they will receive messages! Is this a daily message, weekly message, or monthly message? Does something specific trigger a message?
Most recipients don’t like receiving messages every single day. The carriers actually recommend 4 or less per month, especially for marketing or political use cases.
If you’re seeing an increasing number of opt-outs each time you send a message blast, it's probably time to reevaluate how often you’re sending blasts out, the quality standards of your content, and the degree to which your opt-in processes are up-to-date.
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Frequently asked questions
Why was my SMS campaign flagged as spam?
Carrier filters flag SMS as spam when messages look like unsolicited promotional blasts, lack proper opt-in consent, include spammy keywords, or violate carrier A2P policies.
What are common triggers for spam filtering?
Common triggers include missing opt-in language, vague or misleading calls to action, excessive sending volume from new numbers, use of suspicious keywords (like “free money”), and unregistered A2P traffic.
How can I improve deliverability for my SMS campaigns?
Improve deliverability by ensuring explicit opt-in from recipients, clear opt-out instructions, clean formatting, A2P traffic registration where required, and pacing messages to avoid volume spikes.
What is A2P registration and why does it matter?
Application-to-Person (A2P) registration is a requirement in many regions for high-volume messaging. Registering your traffic with carriers gives them metadata about your use case and helps avoid filtering.
Can using verified sender IDs help reduce spam flags?
Yes — using properly configured and verified sender IDs or dedicated numbers, along with compliant content practices, can improve trust and reduce the likelihood of messages being flagged.
