One-way A2P (Application-to-Person) SMS is a type of message sent from a business or system to a user without allowing the recipient to reply. It's commonly used for delivering time-sensitive information such as one-time passwords (OTPs), appointment reminders, transaction alerts, or promotional messages. This method ensures efficient, reliable communication at scale, especially when immediate user action is required.

Short Codes are 5–6 digit numbers used for high-volume, one-way or two-way messaging like alerts or OTPs. They're fast and reliable but costlier and require carrier approval. Long Codes (10-digit numbers) are suited for lower-volume, two-way communication such as customer support or appointment confirmations. Alphanumeric Sender IDs display a brand name as the sender. They're typically used for one-way messages like promotions or notifications and don't support replies.

A2P messaging is governed by strict regulations to ensure a positive user experience and prevent misuse. Key restrictions include: Content Compliance (messages must adhere to local laws and industry guidelines, avoiding any prohibited, deceptive, or sensitive content), Regional and Carrier Rules (restrictions vary by country and carrier), Message Throughput (sending limits may apply depending on the channel used, e.g. short code, long code, or toll-free numbers), and Quiet Hours (some regions enforce "quiet hours" during which marketing or promotional messages are restricted).