Understand Bulk SMS Throughput and Campaign Timing
Understand Bulk SMS Throughput and Campaign Timing
Sending a bulk SMS campaign to 5,000 contacts? It will take approximately 83 minutes to deliver all messages. Understanding how throughput works helps you plan campaign timing and set realistic expectations for delivery windows.
Available on: Pro plan and above (Bulk SMS)
How Bulk SMS Delivery Works
JustCall sends bulk SMS messages at a rate of 1 message per second. This is a system-level rate, not a carrier-imposed limit.
What that means in practice
| Campaign size | Approximate delivery time |
|---|---|
| 100 contacts | ~2 minutes |
| 500 contacts | ~8 minutes |
| 1,000 contacts | ~17 minutes |
| 2,500 contacts | ~42 minutes |
| 5,000 contacts | ~83 minutes |
These are approximate times. Actual delivery may vary based on carrier processing, time of day, and message content.
Carrier Throughput Limits (US Only)
In the US, carrier throughput is determined by your 10DLC Trust Score — a rating assigned when you register your brand for A2P messaging. Higher trust scores mean more messages per second across carriers.
Explicitly declared use cases
| Trust Score | Total SMS/second | AT&T | T-Mobile | Verizon |
|---|---|---|---|---|
| 75-100 | 225 | 75 | 75 | 75 |
| 50-74 | 225 | 75 | 75 | 75 |
| 1-49 | 12 | 4 | 4 | 4 |
| 0 (Low Volume Standard) | 12 | 4 | 4 | 4 |
Low Volume Mixed campaigns
Low Volume Mixed campaigns have a fixed throughput of 3.75 messages per second (1.25 per major carrier), regardless of trust score.
Note: JustCall's system rate of 1 message/second is typically the bottleneck, not carrier limits. Carrier throughput becomes relevant only when carriers throttle below 1 message/second, which can happen with low trust scores or flagged content.
Plan Your Campaign Timing
Schedule for off-peak hours
Send campaigns during business hours in your contacts' time zones. Messages sent at 2 AM are less likely to get a response and may feel intrusive.
Account for delivery windows
If you need all 5,000 messages delivered before a 10 AM deadline, start the campaign no later than 8:37 AM. Build in a buffer for carrier delays.
Break large campaigns into batches
For campaigns larger than 5,000 contacts, break them into batches. Each batch sends sequentially at 1 message/second.
Factors That Affect Delivery
| Factor | Impact |
|---|---|
| Trust Score | Low trust scores can cause carrier throttling beyond JustCall's system rate |
| Message content | Messages with URLs, special characters, or flagged keywords may be filtered |
| Time of day | Carrier networks may process messages more slowly during peak hours |
| 10DLC registration status | Unregistered US numbers face severe throughput restrictions |
CAUTION: T-Mobile imposes separate daily message limits beyond throughput rates. If your campaigns target a large number of T-Mobile subscribers, monitor delivery reports for throttling.
Related Articles
- Create and Manage SMS Templates — reusable message templates for campaigns
- Managing SMS Conversations in JustCall — manage replies from bulk campaigns in your inbox