yinheli / smtp-email-forward

A simple smtp server

smtp-email-forward

This is a simple smtp server that can be hosted in a docker container and be used to forward the email to another address. This project is part of the blog post Simple SMTP server to forward your emails.

Features

• receive email multiple domains
• save emails to GCP bucket
• forward the emails to another address using mailgun

Build and run

# clone the repository
git clone https://github.com/gabihodoroaga/smtp-email-forward.git
# build
cd cmd
go build

In order to run the project you need to create also a GCP bucket

GCP_BUCKET=smtpd-email-forward-123
gsutil mb -c nearline gs://$GCP_BUCKET

and a service account

# create the service account
gcloud iam service-accounts create smtpd-email-forward-123 \
    --description="A service account to write to the bucker" \
    --display-name="smtpd-email-forward-123"
# grab the email
GCP_SERVICE_ACCOUNT=$(gcloud iam service-accounts list --format="value(email)" --filter="displayName=smtpd-email-forward-123")
# give the service account the permission to create objects
gsutil iam ch serviceAccount:$GCP_SERVICE_ACCOUNT:objectCreator gs://$GCP_BUCKET
# create and save the service account key
mkdir certs
gcloud iam service-accounts keys create certs/gcpServiceAccount.json \
  --iam-account $GCP_SERVICE_ACCOUNT

and the service certificates

openssl req -x509 -newkey rsa:4096 -keyout ./certs/server.key -out ./certs/server.crt -days 365 -nodes

In order to test he mailgun integration you need to create a new mailgun account and to setup MAILGUN_DOMAIN and MAILGUN_API_KEY environment variables

Authors

Gabriel Hodoroaga hodo.dev

Referenced projects

• github.com/mhale/smtpd
• github.com/ilyakaznacheev/cleanenv
• go.uber.org/zap

TODO

• add support for SPF validation
• add support for DKIM validation
• add options to filter the emails addresses
• add support for Let's encrypt