smtp-relay

smtp-relay

This project replace a previous project aws-smtp-relay

The goal is to have a dynamic SMTP server that can either be used to run a debug SMTP locally that just store received email in a folder Or relay a SMTP protocol to an SES API call (goal of aws-smtp-relay) Or simulate some Incoming capabilities of AWS SES, like mail2s3 or mail2sqs and similar mail2gcpstorage and mail2gcppubsub

Quick Start

Replace aws-smtp-relay

Run with a configuration file:

// Replace my previous project aws-smtp-relay
{
  "flows": {
    "localhost": {
      "filters": [
        // Allow any ip to use the SMTP
        {
          "type": "whitelist",
          "ips": ["regexp:.*"]
        }
      ],
      "outputs": [
        {
          "type": "aws",
          // Send it to SES
          "ses": {}
        }
      ]
    }
  },
  "options": {
    "disableReverseLookup": false,
    // Do not require auth
    "authOptional": true,
    "logger": true
  }
}

SMTP 2 GCP Storage

{
  "flows": {
    "localhost": {
      "filters": [
        // Allow any ip to use the SMTP
        {
          "type": "whitelist",
          "to": ["regexp:.*@mydomain.com"]
        }
      ],
      "outputs": [
        {
          "type": "gcp",
          // Store it in the bucket
          "path": "gs://myemail/",
          // Send a message to the queue containing the bucket url if exist and the metadata of the email
          "pubsub": ""
        }
      ]
    }
  },
  "options": {
    "disableReverseLookup": false,
    // Do not require auth
    "authOptional": true,
    "logger": true
  }
}

Run it locally for dev

You can just leveraging the Docker image

docker run -p 10025:10025 -v `pwd`/emails:/smtp-relay/received_emails ./configs/fake-smtp.jsonc

Concepts

The smtp server is subdivided with:

• Filters
• Core
• Processors
• Flows

Filters

These components decide to accept or refuse an email.

At each SMTP command step, they can make a decision to refuse or accept an email or not make a decision boolean|undefined

By default, two filters exist:

• whitelist: allow emails based on regexp or exact values
• http-auth: proxy the decision on the email to an HTTP endpoint

Processors

These components receive the email sent after it was accepted by the filters.

There is 4 types:

• aws:
• gcp:
• file:
• mailer:

Flows

A flow is defined within the configuration, it defines the filters and the outputs to apply if the message match the filters

You can have as many flow as you desire within the SMTP server

Core

Manage the coordination of different component and is in charge of capturing the mail stream

Common variables available for replacements

iso8601: date and time in YYYYmmddHHiiss format

timestamp: UNIX timestamp

id: Session id

The following variables are not always available but should be within processors

from: Email of the sender

messageId: Message id

subject: subject of the email

to: list of recipient comma separated