A2P 10DLC is the US carrier framework for application-to-person texting over ten-digit local numbers. It requires businesses to register who they are and what they'll text about before sending automated SMS. Registered traffic gets better deliverability; unregistered traffic gets filtered, throttled, or blocked by the carriers.
Breaking down the acronym
A2P means "application to person" — messages sent by software (a CRM, an AI assistant, an appointment reminder system) rather than a human tapping on a phone. 10DLC means "ten-digit long code" — a standard local phone number, as opposed to a short code or toll-free number.
Put together: any business texting customers through software from a local number falls under A2P 10DLC rules in the United States.
Why carriers created it
For years, spammers abused cheap local numbers to blast unwanted texts. Carriers responded by building a registration system: every business (a "brand") and every messaging use case (a "campaign") must be declared and vetted before traffic flows. In exchange for transparency, legitimate registered senders get higher throughput and far fewer filtered messages. Unregistered senders increasingly get their messages silently dropped.
What registration actually involves
At a high level, there are two steps. First, brand registration: the business's legal name, EIN, address, and contact details are submitted and verified. Second, campaign registration: you describe the type of messages you'll send (lead follow-up, appointment reminders, promotions), provide sample messages, and explain how contacts opt in. For agencies, this means every client sending texts needs their own brand and campaign — you can't run all clients through one registration.
Go deeper: Read the full A2P 10DLC guide for agencies, or start with the pillar on SMS compliance.