When you send an SMS campaign, the platform dispatches messages through a background queue. The queue has a send rate. Most accounts send at a standard rate. Accounts on a particular phone carrier or number type send at a lower rate, meaning messages go out more slowly across the same time window.

The send rate is determined by the telecom provider your sending number is registered with, not by anything you configure in the campaign itself. If your number uses a provider with a lower send rate, your campaign automatically uses the low-throughput queue. You do not need to select this or opt in.

For small campaigns the difference is not perceptible. For large campaigns, a low-throughput send takes longer to complete. The campaign status will show as "Sending" for a longer period before it transitions to "Sent." All other behavior is identical: quiet-hours enforcement still applies (messages are held and sent after 9am Eastern if you send late at night), unsubscribes are still honored, and merge fields still resolve per recipient.

Different telecom providers impose different rate limits on how many messages can be submitted per second through their APIs. The platform respects those limits automatically to avoid rejected or dropped messages. Using a separate queue for lower-throughput providers keeps standard-rate campaigns from being slowed down when both run at the same time.