What is SMS Deliverability?
SMS deliverability is the measure of how successfully your text messages reach their intended recipients. Unlike email, where messages can land in spam folders, undelivered SMS messages simply disappear — your recipients never see them, and you may not even know they failed.
For businesses sending transactional messages (verification codes, appointment reminders, shipping updates) or marketing campaigns, poor deliverability directly impacts customer experience and revenue. A 95% delivery rate might sound good, but if you're sending a million messages a month, that's 50,000 customers who never received your message.
Factors Affecting SMS Delivery
1. Carrier Routing
Every SMS travels through multiple carriers and aggregators before reaching the recipient's phone. The path a message takes affects delivery speed, cost, and success rate. Messages routed through unreliable aggregators may be delayed, filtered, or dropped entirely.
Message Provider Lookup identifies which company handles SMS delivery for any phone number. This information helps you understand your routing options and troubleshoot delivery issues.
See your message routing. Use our Message Provider API to identify SMS carriers for any number.
Learn More2. Sender Reputation
Carriers track the behavior of senders and assign reputation scores. Senders with poor reputations face higher filtering rates and may be blocked entirely. Reputation is affected by:
- Complaint rates — How often recipients report messages as spam
- Opt-out rates — How many people unsubscribe after receiving messages
- Bounce rates — How many messages go to invalid numbers
- Volume patterns — Sudden spikes in sending volume raise red flags
3. Content Filtering
Carriers use automated systems to filter SMS content for spam, fraud, and prohibited content. Messages containing certain keywords, URL shorteners, or patterns associated with spam may be blocked. Common triggers include:
- Financial terms (loan, credit, debt) without proper 10DLC registration
- URL shorteners (bit.ly, tinyurl) — use branded short links instead
- ALL CAPS text or excessive punctuation
- Phrases commonly used in spam ("Free", "Winner", "Act now")
4. Number Type
Different phone number types have different SMS capabilities:
- Wireless — Native SMS support, highest delivery rates
- Landline — May support SMS via text-to-speech or not at all
- VoIP — Varies widely by provider; some support SMS, many don't
Knowing the line type before sending helps you avoid wasted messages and choose appropriate fallback channels (voice, email) for numbers that can't receive SMS.
10DLC Registration
10DLC (10-Digit Long Code) is the industry standard for business SMS in the United States. All US carriers now require businesses to register their brand and campaigns before sending A2P (Application-to-Person) messages from standard phone numbers.
Registration Requirements
- Brand Registration — Register your business with The Campaign Registry (TCR)
- Campaign Registration — Register each use case (marketing, transactional, etc.)
- Number Assignment — Assign phone numbers to approved campaigns
Benefits of 10DLC
- Higher throughput (messages per second) than unregistered numbers
- Lower filtering rates from carriers
- Better sender reputation over time
- Compliance with carrier requirements
Read our complete 10DLC Registration Guide →
A2P vs P2P Messaging
Understanding the distinction between A2P and P2P messaging is crucial for compliance:
- A2P (Application-to-Person) — Messages sent from business applications to consumers. Includes marketing, notifications, verification codes, and any automated messages. Requires 10DLC registration.
- P2P (Person-to-Person) — Standard text messages between individuals. Not subject to 10DLC requirements but has stricter volume limits.
Sending A2P traffic over P2P channels violates carrier terms and will result in filtering or blocking. Learn more about A2P vs P2P messaging →
Improving SMS Delivery Rates
Pre-Send Validation
Before sending any message, validate the recipient number:
- Format validation — Ensure the number is properly formatted for the destination country
- Line type check — Verify the number can receive SMS (wireless vs landline)
- Carrier lookup — Identify the current carrier for optimal routing
- Activity check — Detect disconnected or reassigned numbers
Validate numbers before sending. Our API checks line type, carrier, and activity status in real-time.
Get Free API KeyOptimize Message Content
- Keep messages concise (160 characters or less avoids message splitting)
- Use your registered business name as the sender
- Include clear opt-out instructions (STOP to unsubscribe)
- Avoid spam trigger words and excessive capitalization
- Use full URLs or branded short links instead of generic shorteners
Monitor and Iterate
Track delivery metrics and adjust your approach:
- Delivery rate — Percentage of messages successfully delivered
- Failure reasons — Why messages fail (invalid number, carrier block, etc.)
- Time to deliver — How long messages take to reach recipients
- Opt-out rate — Track unsubscribes to gauge message quality
Message Provider Lookup
Message Provider Lookup identifies which company handles SMS delivery for any phone number. This is different from carrier lookup — while the carrier owns the number, a different company (the message provider) may handle actual SMS routing.
Why It Matters
- Routing decisions — Choose the best path to reach each recipient
- Troubleshooting — Identify where delivery issues occur
- Cost optimization — Route through the most cost-effective paths
- Compliance — Understand which aggregators handle your traffic
Learn more about Message Provider Lookup →
Common Delivery Issues and Solutions
| Issue | Cause | Solution |
|---|---|---|
| Messages not delivered | Invalid numbers, carrier blocks | Validate numbers before sending; check 10DLC registration |
| Delayed delivery | Carrier congestion, poor routing | Use message provider lookup to optimize routing |
| High opt-out rates | Poor targeting, excessive frequency | Segment audiences; reduce send frequency |
| Filtered as spam | Content triggers, poor reputation | Review content; complete 10DLC registration |
| Landline failures | Sending SMS to non-SMS numbers | Check line type before sending |
Read our SMS Delivery Troubleshooting Guide →
Frequently Asked Questions
What is a good SMS delivery rate?
A good SMS delivery rate is 95% or higher for validated, opted-in recipients. Rates below 90% indicate issues with list quality, carrier filtering, or routing. Transactional messages (verification codes, alerts) typically see higher rates than marketing.
Why are my SMS messages not being delivered?
Common causes include: invalid or disconnected numbers, sending to landlines that don't support SMS, carrier content filtering, missing 10DLC registration, or poor sender reputation. Validate numbers before sending and ensure your campaigns are properly registered.
Do I need 10DLC registration to send SMS?
Yes, if you're sending A2P (business) messages in the United States from 10-digit phone numbers. All major US carriers require 10DLC registration. Unregistered senders face severe filtering and low throughput limits.
What is the difference between A2P and P2P messaging?
A2P (Application-to-Person) messaging is automated business messaging sent from software applications, including marketing, notifications, and verification codes. P2P (Person-to-Person) is standard texting between individuals. A2P requires 10DLC registration; P2P does not.
How can I check if a phone number can receive SMS?
Use a phone intelligence API to check the line type. Wireless numbers support SMS natively. Landlines may support SMS via text-to-speech services. VoIP numbers vary by provider. VeriRoute Intel's API returns line type, carrier, and message provider information.