How to Manage SMS Volume Across Multiple Carriers

Step 1: Understand Carrier Throughput Limits

Every US carrier imposes message-per-second or message-per-minute limits on inbound SMS from each sending number. These limits are not publicly documented with exact numbers, but they are enforced consistently. The limits depend on your 10DLC campaign's trust score, the carrier's current traffic load, and the SMS provider you are routing through.

Practical throughput ceilings for a single 10-digit sending number:

• Low trust score campaigns: Approximately 1-4 messages per second across all carriers combined. A 10,000-message campaign takes 40+ minutes at this rate.
• Medium trust score campaigns: Approximately 10-15 messages per second. The same 10,000 messages complete in roughly 12 minutes.
• High trust score campaigns: 30+ messages per second. Large campaigns complete quickly, but even at this tier, single-number sending hits a ceiling on very large lists.

The key insight is that these limits apply per sending number per carrier. If your list is 60% T-Mobile, 25% AT&T, and 15% Verizon, you will hit the T-Mobile limit long before the AT&T or Verizon limits. Your effective throughput is bottlenecked by whichever carrier has the largest share of your list.

Step 2: Distribute Across Sending Numbers

The most direct way to increase throughput is using multiple sending numbers. If one number can send 10 messages per second, five numbers can send 50. Each number has its own independent rate limit with each carrier.

When setting up multiple sending numbers:

• Register all numbers under the same 10DLC campaign. This keeps them under one brand identity and avoids compliance issues. Adding numbers to an existing campaign is straightforward through your TCR registration.
• Distribute messages evenly. If you have 5 sending numbers and 10,000 messages, each number should handle approximately 2,000 messages. Uneven distribution means one number hits its rate limit while others sit idle.
• Use numbers from different area codes. Some carriers apply additional scrutiny when multiple messages arrive from numbers in the same area code. Geographic diversity in your sending numbers reduces this risk.

The platform handles number rotation automatically when you configure multiple sending numbers for a campaign. Messages are distributed across your available numbers without manual assignment.

Step 3: Use Carrier-Based Routing

Carrier-based routing multiplies your effective throughput in a different way than adding sending numbers. Instead of increasing how many messages you can send per second, it improves how many of those messages actually arrive.

When routing through a single SMS provider, your throughput to any given carrier is limited by that provider's connection to that carrier. If your provider has a strong AT&T connection but a weaker T-Mobile connection, your T-Mobile delivery will lag even if you have plenty of sending numbers.

With 12-provider carrier-based routing, messages to each carrier flow through the provider with the strongest direct connection. T-Mobile messages go through a T-Mobile-optimized provider, AT&T messages through an AT&T-optimized provider, and so on. This means:

• Higher per-carrier throughput because each provider's best routes are used
• Automatic failover when any single provider experiences congestion
• Parallel delivery across providers, so your total throughput scales beyond any single provider's capacity

Step 4: Pace Your Sends

Even with multiple sending numbers and carrier-based routing, sending too many messages too fast triggers carrier-level velocity filters. These filters detect sudden spikes in message volume from a brand or sending number pattern and respond by increasing filtering aggressiveness on subsequent messages.

Effective pacing strategies:

• Ramp up gradually. If you normally send 5,000 messages per campaign and want to send 50,000, do not jump straight to the higher volume. Increase by 20-30% per campaign over several sends so carriers see a gradual growth pattern rather than a suspicious spike.
• Spread large campaigns across time windows. Instead of sending 50,000 messages in a single burst, use scheduled sends to deliver in batches of 10,000-15,000 across several hours. This keeps your per-minute rate well within carrier limits.
• Avoid sending everything at the top of the hour. Many senders schedule campaigns to start at round times like 10:00 AM or 2:00 PM. Carrier networks experience the highest load at these times. Starting at off-peak minutes like 10:07 or 2:13 reduces the chance of hitting congestion-related throttling.

Step 5: Monitor Delivery Per Carrier

Aggregate delivery rates hide carrier-specific problems. A campaign showing 88% overall delivery might be delivering 95% to Verizon and AT&T but only 65% to T-Mobile. Without per-carrier monitoring, you would not know that T-Mobile is filtering your messages until you notice lower response rates from a large segment of your list.

Key metrics to track per carrier:

• Delivery rate: Percentage of messages confirmed delivered versus total sent to that carrier. A sudden drop on one carrier while others remain stable points to a carrier-specific routing or filtering issue.
• Delivery speed: How quickly messages reach recipients on each carrier. Increasing latency on one carrier indicates you are approaching that carrier's rate limits for your sending number or provider.
• Failure codes: When carriers return error codes, they indicate the specific reason for rejection. Codes related to rate limiting, content filtering, and sender verification each require different corrective actions.
• Opt-out rate by carrier: Unusually high opt-out rates from one carrier's subscribers might indicate that your messages are arriving differently on that carrier, such as being delivered to a spam or promotional folder on carriers that support message categorization.

Review per-carrier metrics after every campaign, not just when problems appear. Gradual degradation on one carrier is easier to fix early than after it has been declining for weeks. If you see a carrier-specific drop, check whether the issue is deliverability-related or an active blocking situation.