Relayer Infrastructure

An overview of the relayer infrastructure for Email Wallet, and how to set it up.


The Relayer, a crucial system component, bridges email communication and blockchain transactions, ensuring secure information processing.

Below is a diagram of the Relayer infrastructure and its component interactions.

To build the Relayer, you need to understand its three main components:

  • SMTP Server: The entry point for emails, which the Relayer monitors for incoming messages that trigger blockchain transactions.

  • Relayer: The core service that listens for emails from the SMTP server, communicates with the Prover to verify proofs, and then writes the validated transactions to the blockchain.

  • Prover: A separate service that the Relayer relies on to verify and create zk proofs of the data extracted from emails.

  • Database (DB): A PostgreSQL database to store account information, facilitating checks on whether an account already exists within the system.

Building the Relayer


Before building the Relayer, ensure that you have the following prerequisites installed:

  • Node.js and npm

  • Python 3

  • Docker

  • Rust and Cargo (with build-essential or equivalent for your operating system)

For Ubuntu users, you can install build-essential by running:

sudo apt-get update
sudo apt-get install build-essential

For macOS users, you can install the necessary tools by installing Xcode Command Line Tools:

xcode-select --install

Running the Prover

☞ Running locally

To run the prover locally, follow these steps:

  1. Prepare the Environment: Ensure your system has Node.js, npm, and Python 3 installed. The prover relies on specific npm packages and Python modules to function correctly.

  2. Install Global npm Packages: Install snarkjs globally using npm.

   npm install -g snarkjs@latest
  1. Install Python Requirements: Navigate to the prover directory and install the required Python packages listed in requirements.txt.

 pip install -r requirements.txt
  1. Run the curl commands and script in the prover/ file.

  2. Start the prover

python3 packages/prover/

☞ Using Modal

The prover leverages Modal, a cost-effective, serverless computing platform activated as needed, for generating zk proofs. Visit site here:

  1. Set Up Modal Tokens: Follow the instructions in /Relayer.Dockerfile to set up your Modal tokens.

  2. Start the Prover Service: Run the following command to start the Prover service using Modal:

modal run python packages/prover/

Setting up the DB

Database Setup Steps:

  1. Start PostgreSQL Database:

    docker run --rm --name email-wallet-db -e POSTGRES_PASSWORD=p@ssw0rd -e POSTGRES_USER=emailwallet -e POSTGRES_DB=emailwallet -p 5432:5432 postgres
  2. Set Environment Variable: In .env:


Note: The system triggers on emails with accountKey in the subject, for new account setups. Reply-email functionality for account transport will be deprecated.

Setting up the Relayer

  1. Create a .env file in packages/relayer by taking a copy from .env.example.

cp packages/relayer/.env.example packages/relayer/.env
  1. Update the .env file

CORE_CONTRACT_ADDRESS=           # Address of the deployed wallet contract.
PRIVATE_KEY=                      # Private key for Relayer's account.
CHAIN_ID=11155111                    # Chain ID of the testnet.

# IMAP + SMTP (Settings will be provided by your email provider)
LOGIN_ID=                    # IMAP login id - usually your email address.
LOGIN_PASSWORD=""         # IMAP password - usually your email password.

PROVER_LOCATION=local         # Keep this local for running the prover locally.
PROVER_ADDRESS="" # local or modal URL

FEE_PER_GAS=0        # Fee per gas in wei.
DATABASE_URL= "postgres://test@localhost/emailwallet_test"
CIRCUITS_DIR_PATH=  #Path to email-wallet/packages/circuits
INPUT_FILES_DIR_PATH=  #Path to email-wallet/packages/relayer/input_files
EMAIL_TEMPLATES_PATH=  #Path to email templates, e.g. ./packages/relayer/eml_templates/

ONBOARDING_REPLY="You received 100 TEST!"



Buidling the Docker image

  • For local development

cd ../../
docker buildx build -t email_wallet_v1_relayer:latest-arm -f Relayer.Dockerfile . \
  --build-arg modal_token_id=${MODAL_TOKEN_ID} \
  --build-arg modal_token_secret=${MODAL_TOKEN_SECRET}
  • Production(x86 compatibility):

docker buildx build -t email_wallet_v1_relayer:latest -f Relayer.Dockerfile . \
  --build-arg modal_token_id=${MODAL_TOKEN_ID} \
  --build-arg modal_token_secret=${MODAL_TOKEN_SECRET} \

Running the Relayer

  1. Start the Docker Container: Launch the Relayer service in a Docker container with the following command:

docker run \
-p 80:80 \
-v $(pwd)/.env:/email-wallet/packages/relayer/.env \
  1. Update Contract ABIs: Ensure the contract ABIs are up to date in packages/relayer/abi/ directory.

  2. Register the relayer on chain by running:

cargo run --release -- setup

This step registers the relayer's details on the blockchain, preparing it for operation.

  1. Start the relayer:

cargo run --release
  1. You can test by sending an email to your relayer account with a subject like Send 1 ETH to Relayer will deploy wallet for you for the first time and you will need to fund it externally as the wallet have no balance.

☞ Running Relayer as Docker container

Building Docker Image

For local development

cd ../../
docker buildx build -t email_wallet_v1_relayer:latest-arm -f Relayer.Dockerfile . \
  --build-arg modal_token_id=${MODAL_TOKEN_ID} \
  --build-arg modal_token_secret=${MODAL_TOKEN_SECRET}

For x86 compatibility(e.g. For production)

cd ../../
docker buildx build -t email_wallet_v1_relayer:latest -f Relayer.Dockerfile . \
  --build-arg modal_token_id=${MODAL_TOKEN_ID} \
  --build-arg modal_token_secret=${MODAL_TOKEN_SECRET} \

Create .env

Create .env in the execution directory with reference to env_example.

How to Run

docker run \
-p 80:80 \
-v $(pwd)/.env:/email-wallet/packages/relayer/.env \
-e SETUP=false

☞ Relayer's Incentive

The Relayer's incentive is transaction fees collected from the sender. Specifically, the Relayer operator can set a fee per gas in wei to the ENV file. However, that value must be less maxFeePerGas parameter defined in our contract, which is 2 gwei now.

When the Relayer posts the email-triggered transaction along with the ZK proof of email, our contract calculates the total amount of fee in wei as follows:

  1. If the transaction does not pass the validation function validateEmailOp, the fee is zero.

  2. The contract measures the consumed gas when executing the transaction.

  3. The gas to refund ERC20 tokens, 55000 gas, is added to 2.

  4. If the transaction specifies a recipient's email address, 450000 and 500000 gas are added to 3 for ERC20 tokens transfer and the other use cases, respectively.

  5. The total amount of fee in wei is the multiplication between the fee per gas set by the relayer and the total gas in 4.

Note that our contract catches any errors during the execution of the transaction in Step 2 instead of making the transaction fail because the Relayer cannot always simulate if the execution returns errors in general cases before posting it on-chain. Therefore, the Relayer can always collect the fee as long as the transaction passes the validation in Step 1. This design refers to the bundler's fee mechanism in ERC-4337.

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