How to Warm Up a New Phone Number to Avoid Filtering

A new phone number with no sending history is treated with suspicion by carrier filtering systems. Warming it up gradually over one to two weeks establishes a clean behavioral baseline that protects your deliverability.

Danial A

Senior Twilio Consultant, Telphi Consulting

June 20, 2026

8 min read

Twilio

Compliance

Deliverability

Carrier filtering systems assign new phone numbers a neutral trust level at provisioning time, which means they are not trusted and not distrusted until behavioral signals accumulate. Sending large volumes of messages from a brand-new number immediately after provisioning mimics the behavior pattern of spam operators who rapidly cycle through numbers to avoid blocking, and carriers apply aggressive filtering to exactly that pattern. A proper warm-up process involves gradually increasing send volume over the first one to two weeks while monitoring delivery and complaint rates to establish a positive behavioral baseline that carriers recognize as legitimate.

Why Warm-Up Matters Even for Registered Numbers

Completing A2P 10DLC registration improves your baseline trust level with carriers, but it does not eliminate the behavioral pattern analysis that carrier systems apply to individual phone numbers. A registered number that suddenly sends 10,000 messages on day one will still see elevated filtering compared to a registered number that built up to that volume over two weeks. This is because registration verifies your identity and use case but does not vouch for your operational behavior, and sudden high-volume sending from a new number is a behavioral signal that filtering systems weight heavily regardless of registration status. Businesses that provision new numbers for a holiday campaign and immediately start sending full volume consistently report lower delivery rates in the first week than businesses that warm the numbers before the campaign date.

A Practical Warm-Up Schedule

The goal of a warm-up schedule is to gradually increase your daily send volume on each new number, starting low enough that complaint rates and filtering signals are minimal even if some recipients react negatively. A reasonable warm-up schedule for a 10DLC number starts at 100 to 200 messages per day in the first two days, doubles every two days through the first week, and then increases by 50% every two days in the second week. By day 14, a number warmed on this schedule can typically handle 2,000 to 3,000 messages per day with stable delivery rates. During warm-up, send only to your highest-quality subscribers, meaning those who have opted in recently and have a history of positive engagement with your communications, not to stale or unconfirmed addresses. Reserve your riskiest or oldest list segments for after the number is fully warmed.

Distributing Volume Across a Number Pool

If your SMS program requires sending 50,000 or more messages per day, a single number cannot handle that volume even at full throughput, and you will need a pool of multiple registered numbers. When building a number pool, provision all numbers simultaneously but warm them on staggered schedules so that each number has its own independent warm-up timeline and you are not sending large volumes on all numbers from day one. Twilio's Messaging Services feature supports pools of numbers with automatic load balancing across the pool, which simplifies the technical implementation of multi-number sending. As you add new numbers to an existing pool, warm each new number independently before activating it in the rotation; adding a cold number to a pool that already has warmed numbers dilutes the pool's average trust level and can reduce overall delivery rates temporarily.

Monitoring Delivery Rates During Warm-Up

During the warm-up period, monitor your Twilio error logs daily for error codes that indicate filtering. Error code 30003 indicates the message was undeliverable due to the phone number being unavailable. Error code 30007 specifically indicates a carrier violation, which is a strong signal that filtering is active on that number and that you should pause sending and investigate the cause before continuing. Error code 30006 indicates a landline number was dialed, which is a list quality issue rather than a filtering issue but inflates your undelivered rate during warm-up. Track the ratio of delivered to undelivered messages as a daily metric and expect it to improve over the warm-up period as the number builds history. If your delivery rate does not improve after two weeks of warming, the issue is likely content or registration rather than a behavioral pattern problem.

Conclusion

Warming up new phone numbers is an operational discipline that takes two weeks but protects months of SMS program deliverability, and skipping it is one of the most common and most preventable deliverability mistakes. Speak with our compliance team and we will build a warm-up plan for your Twilio number pool and monitor your delivery metrics throughout the process.