SMS Troubleshooting Directory
Technical diagnostic trees and guides for debugging SMS delivery failures, carrier filtering, and OTP latencies.
Diagnostic Tree
Why SMS Codes Fail: Delivery Diagnostic Tree
Detailed technical guide explaining carrier filtering, shortcode vs toll-free blocks, 10DLC restrictions, and how to debug OTP delivery failures.
Diagnostic Tree
OTP Delays: Carrier Queue & DND Debugging
Understand telecom routing latencies, Do Not Disturb (DND) regulatory scrubbing, and how to diagnose delayed verification messages.
Diagnostic Tree
VoIP Number Rejection: Line Type Debugging
How Telesign, Twilio Lookup, and Neustar carrier databases identify virtual VoIP lines vs physical SIMs, and what services enforce it.
Diagnostic Tree
Carrier SMS Delays: Causes, Latencies & Triage
How carrier firewalls, queue congestion, and aggregator peering cause SMS delivery latencies.
Diagnostic Tree
10DLC Filtering: Campaign Registration
Understand US carrier 10DLC spam filters, TCR vetting scores, unregistered traffic penalties, and why verification codes are blocked.
Diagnostic Tree
Shortcode Routing: Why Virtual Inboxes Fail
Technical analysis of shortcode routing restrictions, why shortcodes cannot message virtual long-codes, and how to verify 2FA passcodes.
Diagnostic Tree
Alphanumeric Sender ID: US & CA Limitations
Understand why custom alphanumeric sender IDs fail in the US and Canada, and how carrier regulations dictate sender formatting.
Diagnostic Tree
Silent SMS Drops: Carrier Firewalls & DLR
Diagnose silent SMS drops where delivery receipts report success but handset never receives the message. Carrier firewall triage.
Diagnostic Tree
WhatsApp & Telegram: VoIP Verification Blocks
Understand why WhatsApp, Telegram, and Signal reject virtual numbers during registration and how messaging apps enforce phone number security.
Diagnostic Tree
Bank 2FA Blocks: Shortcodes & Wireless SIMs
Why Chase, Bank of America, Wells Fargo, and PayPal reject virtual numbers for two-factor authentication. FFIEC and NIST standards.
Diagnostic Tree
SMS Character Splitting: GSM-7 vs UCS-2
Diagnose unexpected SMS segment billing spikes and character corruption caused by GSM-7 vs UCS-2 encoding mismatches and Unicode characters.
Diagnostic Tree
DND Registry Scrubbing: Regulatory Latencies
Understand international SMS regulatory scrubbing delays, TRAI DLT template registration, and nighttime messaging curfews.
Diagnostic Tree
Toll-Free SMS: Carrier Verification Blocks
Understand why unverified toll-free numbers (800, 888, 877) face 100% block rates by US carriers and how to achieve toll-free verification.
Diagnostic Tree
Webhook Retry Storms: Exponential Backoff
Architectural guide to handling high-throughput SMS webhooks, preventing retry storms, and implementing idempotent queue workers.