Why messages get blocked or label as SPAM
Learn why outbound SMS messages can be blocked by SPAM filters—even for legitimate businesses—and how common triggers like SHAFT-related content, suspicious links, weak consent/opt-out handling, burst sending, and “snowshoeing” patterns affect deliverability.
Why messages get blocked
Filters look at a combination of content + behavior, + reputation. A block can happen even if you’re a legitimate business.
1) Content triggers (including “SHAFT”)
Messages that include (or strongly imply) SHAFT categories are high-risk and commonly filtered:
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Sex
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Hate
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Alcohol
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Firearms
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Tobacco (often including cannabis-related content as well)
Other content patterns that increase filtering risk:
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Overly “salesy” wording (“free!!!”, “act now”, extreme urgency)
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ALL CAPS / excessive punctuation
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Repeated, identical templates sent to many recipients
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Misleading or unclear intent (recipient can’t tell why they’re receiving it)
2) Link-related filtering (short URLs and suspicious domains)
Links are a major spam signal because scammers commonly use them.
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Public URL shorteners (e.g., bit.ly, TinyURL) are frequently abused and can lead to increased blocks.
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Domains with poor reputation (newly created domains, mismatched domains, unusual TLDs) can also trigger filtering.
3) Weak consent or poor opt-out handling
One of the fastest ways to get filtered is by messaging recipients who:
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never opted in, seems uncertain they opted in, or didn’t opt in for that message type (marketing vs alerts vs OTP), or
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opted out previously (STOP) but continue receiving messages
4) Volume/burst sending (volumetric filtering)
Even “clean” content can be blocked if you:
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send large bursts,
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ramp volume too quickly,
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send repetitive messages at high rates,
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retry aggressively after failures
5) “Snowshoeing” across many numbers
Spreading similar traffic across multiple sending numbers to evade reputation systems (“snowshoeing”) is a common spam pattern that can lead to filtering.