hyperlane-monorepo/solidity/interfaces/IMailbox.sol

// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity >=0.8.0;

interface IMailbox {
    function localDomain() external view returns (uint32);

    function dispatch(
        uint32 _destinationDomain,
        bytes32 _recipientAddress,
        bytes calldata _messageBody
    ) external returns (bytes32);

    function process(bytes calldata _metadata, bytes calldata _message)
        external;

    function count() external view returns (uint256);

    function root() external view returns (bytes32);

    function latestCheckpoint() external view returns (bytes32, uint256);
}