A throughput limit (AKA rate limit) refers to the number of A2P text messages you are able to send within a specific period of time based on the following factors:

• Whether or not you’ve verified your Toll-Free messaging traffic or registered your 10-digit long code (10DLC) messaging traffic. If you haven’t verified or registered, which is mandatory, you are sending messages from the Person-to-Person (P2P) pathway, instead of Application-to-Person (A2P). The P2P pathway is designated for everyday interactions between people – the throughput limit for P2P messaging is 60 messages per minute. This is plenty sufficient for the P2P use case but is extremely limiting for business, or A2P, use cases.
• Which Carrier, or Mobile Network Operator (MNO), your end user (or message recipient) is using. Verizon is monitoring throughput by messages sent per second; AT&T by messages sent per minute. T-Mobile, on the other hand, has a daily cap, monitoring messages sent per day.

Throughput limits were established to both prevent the MNOs’ systems from being overwhelmed or bottlenecked, and protect the end user from unsolicited messages and/or SPAM.