SMS Deliverability Best Practices

Last updated 8 days ago

Carriers actively monitor message content, volume, and sending behavior, and messages that do not meet their standards may be filtered or blocked before they arrive. In Subflow, following deliverability best practices means your outreach reaches patients reliably and your account stays in good standing with carriers.

This guide covers what to write and how to structure messages, to maintain high deliverability.

Identity and consent

The first two practices establish trust with both the patient and the carrier before a message is read.

  • Identify yourself in every first message: Always include your organization or clinic name when contacting a patient for the first time. Recipients should immediately recognize who the message is from.

    • Do: "Hi [Name], this is [Clinic Name]. You have an appointment tomorrow at 9:00 AM."

    • Avoid: "Hi, your appointment is tomorrow at 9:00 AM.".

  • Only message contacts who have opted in: Send messages only to contacts who have given clear, documented consent to receive communications from you. Subflow supports consent collection through forms and contact records.

    • Do: Message contacts who completed an intake Form with a messaging consent option.

    • Avoid: Adding contacts to a segment and messaging them before consent is on file.

Message content

Carrier filters evaluate the words, formatting, and links inside every message. The following practices reduce the risk of messages being flagged or blocked.

  • Use natural, conversational language: Carriers expect messages to resemble person-to-person conversations. Avoid repetitive content, ALL CAPS, excessive emojis, or unusual formatting that signals bulk or automated messaging.

    • Do: "Hi [Name], we wanted to check in after your visit. How are you feeling?"

    • Avoid: "ACT NOW!!! Complete your form TODAY, URGENT!!!"

  • Avoid high-risk keywords: Certain words and phrases are more likely to trigger carrier filters. Avoid promotional terms such as "Free," "Earn Money," and "Buy Now."

    • Do: "Your follow-up appointment is ready to schedule."

    • Avoid: "FREE health screening available, act now!"

  • Follow SHAFT content restrictions: Per the Cellular Telecommunications and Internet Association (CTIA), messages must not contain content related to Sex, Hate, Alcohol, Firearms, or Tobacco (SHAFT). Messages containing these references may be blocked by carriers regardless of context. Even in regulated clinical settings, SHAFT-adjacent content requires designated messaging channels and carrier pre-approval.

  • Avoid public URL shorteners: Links from services like Bit.ly are frequently blocked by carriers due to their association with spam and phishing. Use full URLs or links generated directly by Subflow.

Message structure

SMS messages longer than 160 characters may be split into multiple segments, which can affect delivery and readability. Keep messages under 320 characters where possible.

Sending behavior

How and when you send messages affects how carriers interpret your account's activity.

  • Control message volume and frequency: Sending a high volume of identical or repetitive messages in a short period can trigger carrier filtering. Spread out large sends and vary message content to reflect a natural communication pattern.

  • Include opt-out instructions: All outreach messages must give recipients a clear way to unsubscribe. Subflow automatically handles opt-outs when a contact replies STOP.

    • Do: Include "Reply STOP to opt out." in initial outreach and broadcast messages.

    • Avoid: Sending ongoing messages to contacts who have already replied STOP.

  • Provide value in every message: Communicate information that is relevant to what the patient opted in to receive. Unexpected or irrelevant content increases opt-out rates and carrier filtering risk.

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