Where OTPs are used
OTPs are most often used for two factor authentication (2FA) during login, for verifying a new phone number or email address, for authorising sensitive actions like password resets or large payments, and for guest checkout in e-commerce. The user receives a short code, types it back into the app, and the app confirms it matches what was sent.
Why OTPs work
OTPs work because the code is short, has a brief lifetime (usually 5 to 10 minutes), and can only be used once. An attacker who intercepts an old OTP cannot reuse it. The code is also tied to a specific user and channel, so guessing is statistically infeasible at scale.
Best practices for sending OTPs
Use 6 digits, valid for 10 minutes, single-use, rate-limited per phone number or email. Never log or display the code anywhere except to the intended user. Use a dedicated transactional sending channel with priority routing, because OTP delivery time directly affects login conversion.
How Senddio handles OTPs
Tag a send with type:otp and Senddio prioritises the message on its queue, redacts the code in the logs UI, and exposes a deterministic test-mode generator so your continuous integration tests can verify delivery without sending real messages. Typical end-to-end delivery in the US is under three seconds.