> Aztec.nr API reference, v6.0.0 (mainnet and testnet). Index: https://docs.aztec.network/aztec-nr-api/v6.0.0/llms.txt

# Type alias OffchainInboxSync

Module: `noir_aztec::messages::processing::offchain`

```rust
pub type OffchainInboxSync = unconstrained fn(AztecAddress, AztecAddress) -> EphemeralArray<OffchainMessageWithTx>;
```

A function that manages offchain-delivered messages for processing during sync.

Offchain messages are messages that are not broadcasted via onchain logs. They are instead delivered to the recipient by calling the `offchain_receive` utility function (injected by the `#[aztec]` macro). Message transport is the app's responsibility. Typical examples of transport methods are: messaging apps, email, QR codes, etc.

Once offchain messages are delivered to the recipient's private environment via `offchain_receive`, messages are locally stored in a persistent inbox.

This function determines when each message in said inbox is ready for processing, when it can be safely disposed of, etc.

The only current implementation of an [`OffchainInboxSync`](/aztec-nr-api/v6.0.0/noir_aztec/messages/processing/offchain/type.OffchainInboxSync.md) is [`sync_inbox`](/aztec-nr-api/v6.0.0/noir_aztec/messages/processing/offchain/fn.sync_inbox.md), which manages an inbox with expiration and finality-based eviction and automatic transaction context resolution.