SMS campaigns succeed when messages reach your customers' phones. Delivery failures can occur due to missing prerequisites, regional restrictions, carrier filtering, or content violations.
This guide shows you how to diagnose delivery issues and improve campaign performance.
Before You Troubleshoot: Quick Checks
Before investigating delivery issues, verify these prerequisites in your account:
SMS credits balance: Go to Store Settings → SMS Credits Balance. If the balance is 0, SMS messages won't send.
Contact subscription status: Only contacts subscribed to SMS receive campaigns. Check Audience → Segments → Subscription status = Subscribed to SMS.
Phone number format: Numbers must include the country code (e.g., +1XXXXXXXXXX for US, +44XXXXXXXXXX for UK) without parentheses, dashes, or spaces.
Frequency limits: By default, contacts can receive up to 3 SMS per day. Check Store Settings → SMS → Daily sending limits.
Quiet hours: Default quiet hours are 8 PM–8 AM. Messages sent during this window are delayed, not canceled. Check Store Settings → SMS → Quiet hours.
💡 For phone number format, subscription status, and message length issues, see Troubleshoot SMS Channel Issues. For US toll-free verification, see Verify Your Toll-Free Number for SMS.
Troubleshoot SMS Delivery Failures
Understandi "Sent" vs. "Delivered" Status
The "sent" status in your campaign report means the message was successfully transmitted from Omnisend to the carrier. It does not guarantee delivery to the recipient's device.
Delivery failures can occur after the message leaves our system due to:
Carrier filtering or spam detection.
Temporary network issues or the recipient's phone turned off.
Invalid or inactive phone numbers.
Recipient's phone storage is full.
To check actual delivery:
Open Reports → Campaigns (or Reports → Automation).
Click the campaign name.
Scroll to Failed Delivery Rate to see the percentage and number of failed messages.
Click Contact Activity → Select Failed to Deliver (Bounced) to see the list.
Export the list using the Export button.
You can also create a segment: Audience → Segments → Message Delivery Failed → Channel = SMS, then export.
⚠️ Note: If your campaign shows "delivered" or 0% failed delivery but recipients (including you) never receive the SMS, the issue is likely carrier-side filtering or temporary restrictions after the message left Omnisend.
This won't always appear as a failed delivery in reports. Review your campaign content for spam triggers (excessive caps, identical messages, promotional language) and consider spacing out sends or varying message text.
Common Causes of SMS Delivery Failures
1. Regional and Legal Restrictions
Certain countries have strict regulations regarding SMS delivery, which can directly impact your campaigns. For instance:
United Kingdom (UK): SMS campaigns may fail if the sender's ID (SID) has not been whitelisted by local mobile network operators. Once the SID is whitelisted, delivery issues are typically resolved. Learn more.
United Arab Emirates (UAE): All international promotional SMS traffic to the UAE is prohibited. Local promotional traffic is allowed only if the sender is a registered entity in the UAE and complies with local regulations. Noncompliance with these restrictions makes it impossible to send promotional SMS to this region.
China: As of April 2025, SMS messages sent to China from unverified or international senders are subject to very high failure rates (~70%). Learn more about China SMS requirements.
💡 Check more examples: Troubleshoot SMS Channel Issues – Country Restrictions.
2. Sender ID Whitelisting and Formatting Issues
Before sending SMS campaigns, ensure that the sender ID has been approved by the mobile network operators in the destination country. Whitelisting your sender ID is often a necessary step to prevent immediate rejections.
Additionally, incorrect phone number formatting can lead to delivery issues. Always verify that the numbers in your contact list conform to the standard formats required for SMS delivery (international format with country code, no parentheses or dashes).
For US senders: Verify your toll-free number to ensure delivery. Learn how to verify your toll-free number.
3. Deliverability Fluctuations and Carrier Filtering
Deliverability may fluctuate, even after a campaign is sent. Issues such as carrier filtering or temporary restrictions could prevent the SMS from reaching all recipients. Reviewing detailed delivery statistics in the campaign report can provide valuable insights.
Carriers may block messages that appear promotional or bulk. To improve delivery:
Avoid ALL CAPS and excessive exclamation marks.
Don't send more than one promotional message per day per contact.
Include clear unsubscribe links (auto-added for US/CA).
Keep messages under 160 characters.
Vary message content – sending identical messages repeatedly triggers spam detection.
Steps to Troubleshoot and Resolve Delivery Issues
Verify Compliance with Regional Laws: Ensure that your SMS campaigns comply with the legal and regulatory requirements of the target country. Research specific guidelines or consult with Omnisend support for assistance.
Double-Check Contact Lists: Confirm that all intended recipients are subscribed to receive your messages and use valid, correctly formatted phone numbers.
Monitor Campaign Statistics: Review delivery reports to identify patterns or anomalies in delivery status. Go to Reports → Campaigns → [Campaign Name] → Failed Delivery Rate and Contact Activity for detailed status.
Seek Support for Persistent Issues: If issues persist despite compliance and proper formatting, contact our Support Team with relevant details. Provide test cases or specific examples to expedite resolution.
SMS Content Best Practices
Avoid S.H.A.F.T. Violations
To protect recipients, the Cellular Telecommunications and Internet Association (C.T.I.A.) has created a list of prohibited content that shouldn't be included in any SMS – Sex, Hate, Alcohol, Firearms, and Tobacco (S.H.A.F.T.).
SMS marketers use this acronym as a guideline on what not to include in their messages. S.H.A.F.T. guidelines should be taken seriously by anyone using SMS to communicate with their consumers to ensure they are compliant with the C.T.I.A.
Bottom line: S.H.A.F.T. violations are rated as level 0 violations and can permanently terminate your SMS program.
Security Level | Consumer Harm | Cure Date | Penalties |
Level 0 | Extreme harm | Immediate | CTIA: Immediate registry suspension |
Level 1 | Serious harm | 5 business days | CTIA: Unresolved audits, possible registry suspension |
Level 2 | Moderate harm | 5 business days | CTIA: Vary by case |
Note: Currently, S.H.A.F.T. includes CBD, vaping, marijuana/cannabis, and any content relating to each (even though it is not explicitly stated). Be sure to refer to the C.T.I.A. Short Code Monitoring Handbook for more information.
Forbidden Use Cases
Alcohol brands with proper age-gating measures can be verified in compliance with requirements. Please note that robust age gating means that website users must input their date of birth in mm/dd/yyyy format. It cannot be a yes or no question.
Category | Example | Notes |
S.H.A.F.T. use cases and electronic smoking devices | Sex, Hate, Alcohol, Firearms, Tobacco, Vape/E-ciggs | Alcohol traffic is allowed on Toll-Free, Short Code, and Long Code in the US, as long as proper age-gating procedures are in place. Firearms, Tobacco, Vape, and E-cigarettes are not allowed regardless of age gating. |
Using any S.H.A.F.T. content in your SMS will result in:
Your dedicated toll-free number is being blocked on the SMS provider's end.
Money spent on an SMS campaign, with SMS sent but not delivered.
Therefore, in Omnisend, the SMS channel cannot be used for any S.H.A.F.T. content.
General Content Best Practices
Besides S.H.A.F.T. rules, we will also block any messages that violate our Anti-spam policy, which involves illegal activity such as phishing or identity theft scams, unlawful threats, or fraudulent activity.
To comply with C.T.I.A. rules, review the C.T.I.A. Messaging Principles and Best Practices before sending an SMS campaign.
If your SMS campaign didn't break any C.T.I.A. rules, but you or some of your recipients haven't received it, follow these practices:
Use natural language. Avoid non-standard spellings. For example, "H! h0w ar3__you do1ng?" is a non-standard spelling that carriers may flag.
Collect direct consent. You should collect consumer consent yourself and not use consent acquired from a third party. The consumer is expecting a relationship with the business they interacted with.
Set expectations on frequency. Set the proper expectation with the consumer on how many messages they can expect to receive. If you send five texts a month, disclosing "5/msg a month" on the first interaction will result in a positive customer experience.
Include business recognition. Include the business name within the message to ensure that consumers know who they are interacting with.
Keep messages short. SMS stands for "Short Message Service." Even though concatenated messages exist, we recommend not sending more than a 250-character message to keep the medium a short message platform.
Give recipients an option to opt out. We add unsubscribe links for US/CA recipients by default, but not for non-US/CA recipients. Even though adding the Unsubscribe link is optional for non-US/CA recipients, we highly encourage you to add it to the content of your SMS Campaign. SMS marketing is more sensitive than email – the customer can't choose when to check the message. If you want to avoid receiving spam reports or complaints from your customers, allow them to unsubscribe from your marketing.
FAQ
Why does my campaign show "sent" but customers never received the SMS?
"Sent" means the message left Omnisend and was transmitted to the carrier which doesn't guarantee delivery to the recipient's phone. Delivery can fail after sending due to carrier filtering, network issues, invalid numbers, or the recipient's phone being off. To check delivery status, open Reports → Campaigns → [Campaign Name] → Failed Delivery Rate and review Contact Activity for details.
I sent a test SMS to myself, but it never arrived. What's wrong?
Test SMS issues are often caused by frequency limits or carrier spam detection. By default, you can receive up to 3 SMS per day. If you've tested multiple times, you've hit the limit. Also, sending identical messages repeatedly may trigger spam filters.
To fix: change the message text slightly, wait 24 hours, or adjust frequency limits in Store Settings → SMS → Frequency Capping. If testing during quiet hours (8 PM–8 AM), the message is delayed until 8 AM.
Why did I run out of SMS credits faster than expected?
SMS messages longer than 160 characters are split into multiple segments, and each segment uses one credit. For example, a 200-character message counts as 2 credits. Your campaign report shows the number of messages sent, but your credit usage reflects the total segments. To estimate credits before sending, check the Price Estimation step in your SMS campaign editor.
Looking for assistance? Our Support Team is available through in-app chat or at [email protected].