Messaging Rate Limits

SMS (10DLC)

SMS rate limits are determined by your 10DLC campaign type and vetting score. These limits are set by carriers, not by AgentPhone, and apply to all A2P (application-to-person) messaging in the US.

Daily message limits

T-Mobile publishes per-day segment caps based on campaign type and trust score. Since T-Mobile typically represents about one-third of US mobile traffic, you can estimate your total daily capacity by tripling the T-Mobile figure.

High volume vetting scores

High volume campaigns go through a third-party vetting process that assigns a trust score. Your score determines which throughput tier you land in. Companies without an established reputation may initially receive the same 2,000 segment T-Mobile cap as low volume campaigns, even on a high volume campaign. The limit increases as your trust score improves.

Throughput (messages per second)

In addition to daily caps, carriers enforce per-second throughput limits:

Exceeding your limits

When your sending rate or daily volume exceeds carrier limits, AgentPhone queues the excess messages and sends them as capacity frees up. You do not need to implement retry logic on your end. Messages will be delivered in order as throughput becomes available.

For time-sensitive campaigns, plan your send volume against the limits above to ensure messages arrive within your expected window.

Increasing your limits

Your limits are tied to your 10DLC campaign registration and vetting score. To improve your throughput:

1. Register a high volume campaign if you’re currently on low volume or sole proprietor.
2. Schedule a call with us and we’ll help you through the registration and vetting process.

First message requirements

When sending the first outbound SMS to a contact, your message must include:

1. Brand name — identify who is sending the message
2. Opt-in confirmation — acknowledge that the recipient agreed to receive messages
3. Opt-out instructions — tell them how to stop (e.g. “Reply STOP to unsubscribe”)

Example first message:

Hi! This is [Your Brand]. You're receiving this because you signed up
for updates. Reply STOP at any time to unsubscribe.

After the first compliant message, subsequent messages in the same conversation do not need to repeat the opt-in or opt-out language.

Delivery and reliability

All SMS delivery is done on a best-effort basis. A successful API response means the message was accepted by AgentPhone and handed off to the downstream carrier (Sinch), but it does not guarantee delivery to the recipient’s device.

What “delivered” means: Delivery receipts indicate the message was received by the recipient’s carrier network. Once the carrier has the message, final delivery to the device depends on factors outside of AgentPhone’s control.

VoIP-to-VoIP filtering: Messages sent to other VoIP numbers (e.g. numbers provided by Sinch, Twilio, or similar providers) are frequently filtered by the receiving carrier. This is common carrier behavior and there is no error returned when it happens.

iMessage

iMessage limits are based on whether a contact messaged you first and how recently they interacted with your number.

How it works

• Inbound conversations: When a contact messages your number, that counts toward the 1,000 contacts/day/line inbound cap. Once a conversation is open, you can send unlimited replies as long as you respond within 24 hours of their most recent message.
• Follow-ups: If more than 24 hours have passed since a contact’s last message and you initiate a new message, that counts toward the 200 contacts/day/line follow-up cap.
• Limits are per-line: Each phone number has its own independent limits.
• Outbound-first (cold outreach): On outbound iMessage lines, if a contact has never messaged your number before and you message them first, that counts toward a separate outbound-first limit. This is capped at 5 new contacts/day/line by default. Contact the team to increase this limit. Once the contact replies, the conversation is open and follow-up limits apply instead.