You wrote the message, paid for delivery, and the dashboard says “sent.” Then nothing happens. No reply, no click, no signal that a human ever saw it. I’ve watched campaigns where a double-digit slice of the list silently fails, and the team only finds out weeks later when the numbers don’t add up. The frustrating part is that most of these failures are predictable. Here are the ones I run into most, and what actually fixes them.
1. Invalid or mistyped phone numbers
Some numbers just don’t exist. A transposed digit, an extra character pasted from a spreadsheet, a missing country code, and the carrier rejects the message at the door. You usually pay for the attempt anyway.
Fix it by running every number through a phone validation API to check syntax, length, and format before you send. Standardize on E.164 so the same number doesn’t show up three different ways in your data.
2. Landline or VoIP numbers
Not every number can receive a text. Landlines have no SMS path, and plenty of VoIP providers drop inbound SMS by default without telling anyone. Send to those and you’re burning credits on dead ends.
Run line type detection first and only deliver SMS to mobile lines.
3. Suspended or disconnected lines
A number that was valid last quarter can be suspended, deactivated, or sitting in past-due limbo today. Messages to it fail quietly, and you rarely get a clear reason why.
Real-time carrier lookup with deactivation checks catches these before you waste a send on them.
4. Incorrect carrier routing
When your SMS platform routes a message to the wrong carrier, usually because its portability data is stale, the message can fail or vanish without a delivery report. Number portability makes this worse than people expect: the carrier of record is not always the carrier the number originally belonged to.
Use a validation tool with LRN (Local Routing Number) lookup and real-time carrier detection so the message follows the number to its current carrier. CheckThatPhone includes LRN data in its standard API response.
5. Blocked by aggregator or carrier
Carriers block messages from senders or routes they don’t trust, especially when the sender has a weak reputation or skipped the opt-in rules. In these cases you often get no delivery report at all, which makes the problem hard to even see.
Keep your opt-in data clean, drop the spammy phrasing, and register your sender ID where it’s required. Watch performance route by route, because one bad route can drag down an otherwise healthy list.
6. Wrong time or region
Messages sent during quiet hours or into the wrong region get delayed or filtered. Some carriers enforce quiet periods for consumer protection, and a 3am text is a fast way to earn complaints.
GeoIP and timezone data let you send at a sane local hour, which helps deliverability and engagement at the same time.
A note on “action” recommendations
Some validation platforms, CheckThatPhone included, don’t stop at returning raw data. Based on carrier, line status, and history, you get an action field that tells you what to do with the number:
- send: safe to message
- wait: recently suspended, try again later
- skip: unreachable or invalid
That saves you from writing branching logic for every edge case yourself, which is the part most teams get wrong.
Where to start
Guessing is the expensive option here. The single most effective lever is validating numbers before the message ever leaves your system, not auditing failures after the fact. Do that and you stop paying for dead numbers, you stop annoying real people with mistimed texts, and your reported delivery rate starts matching reality.
Read the CheckThatPhone documentation to see how real-time validation and action recommendations work, or explore our pricing plans to start filtering invalid numbers before your next send.