# What is the SMS validity period?

> The validity period is how long an SMSC will keep retrying delivery of a message that didn't reach the handset on first attempt — typically because the recipient was off-network, out of coverage, or had a full inbox. After the validity period expires, the SMSC drops the message and emits an EXPIRED DLR. Default is usually 24 hours; the SMPP submit_sm validity_period field lets you override.

- Canonical URL: https://www.broadnet.me/answers/what-is-validity-period
- Language: en
- Last reviewed: 2026-05-27
- Publisher: BroadNet (https://www.broadnet.me)

## Why it matters for OTPs

An OTP that arrives an hour late is worse than no OTP — the user has already moved on or generated a fresh attempt. For OTP traffic, set validity to 5-10 minutes (validity_period: "000000000500000R" for 5 minutes). If the message doesn't reach the handset in that window, you don't want it eventually arriving stale. For marketing, the operator default (24 hours) is usually fine.

## How operators handle it

Each intermediate SMSC respects the validity it receives and applies it from its own clock — meaning if your aggregator buffers for 2 hours before forwarding, the downstream SMSC sees a validity that's already burned 2 hours of its budget. Mature aggregators stamp validity at submit time but track per-hop budget against the recipient's clock; less mature ones drift, and your 5-minute OTP becomes an effective 3-minute SLO at the handset.

## Validity vs scheduling

Validity is how long after submit the SMSC keeps retrying. schedule_delivery_time (a separate SMPP field) is when the SMSC should first attempt delivery — used for time-zone-aware campaigns. The two are independent: you can schedule a message for 9am local with a 4-hour validity, and the SMSC will retry until 1pm if the first 9am attempt fails.

## Related

- [All answers](https://www.broadnet.me/answers)
- [Glossary](https://www.broadnet.me/answers)
- [What is a DLR (Delivery Receipt)?](https://www.broadnet.me/answers/what-is-dlr)
- [MO vs MT — what's the difference?](https://www.broadnet.me/answers/what-is-mo-vs-mt)
- [What is OTP?](https://www.broadnet.me/answers/what-is-otp)
- [SMS API](https://www.broadnet.me/products/sms-api)