Docker SMTP Server with DKIM 📧

Target of this docker project get easiest way to add smtp to any site in 5 minute.

Setup

Generate DKIM online https://dkimcore.org/tools/
Save privatekey.txt (Private key), publickey.txt (Raw format) and tinydns.txt (Tinydns Format) to folder "dkim".

Replace in tinydns.txt

1533037334.example._domainkey.example.ru.

mail._domainkey.example.ru.

Remove from tinydns.txt all line break, quotes, commas, :3600:: if exist, white spaces.
Must be like this:

mail._domainkey.example.ru:v=DKIM1;p=MIGfMA0GCSqGSIb3DQEBxQUAA4GNADCBiQKBgQCRxzp5nT2S5xqYNPMXaHzx9FZdO+QKiZse6tOTcDeZbRzR9I/oEzMgbuDoWwQ2SsCfvlx7lzxKjDaKkbl3rxnSF1wpSre7AMqM9nZq7b5kX+YzWXzuTiwCMBl6bbnAi/x+qePV9lURJVu5YcblYYOAqWZ/3F/8DDRFGeBjDwcwIDAQAB

Add TXT record to your domain in DNS zone

KEY:

mail._domainkey

VALUE:

v=DKIM1;p=MIGfMA0GCSqGSIb3DQEBxQUAA4GNADCBiQKBgQCRxzp5nT2S5xqYNPMXaHzx9FZdO+QKiZse6tOTcDeZbRzR9I/oEzMgbuDoWwQ2SsCfvlx7lzxKjDaKkbl3rxnSF1wpSre7AMqM9nZq7b5kX+YzWXzuTiwCMBl6bbnAi/x+qePV9lURJVu5YcblYYOAqWZ/3F/8DDRFGeBjDwcwIDAQAB

Delete key from https://dkimcore.org/tools/

Environment variables

The container accepts RELAY_NETWORKS environment variable which MUST start with : e.g :192.168.0.0/24 or :192.168.0.0/24:10.0.0.0/16. The container accepts KEY_PATH and CERTIFICATE_PATH environment variable that if provided will enable TLS support. The paths must be to the key and certificate file on a exposed volume. The keys will be copied into the container location. The container accepts MAILNAME environment variable which will set the outgoing mail hostname. The container also accepts the PORT environment variable, to set the port the mail daemon will listen on inside the container. The default port is 25. To disable IPV6 you can set the DISABLE_IPV6 environment variable to any value.

Build image example:

cd smtp && docker build -t smtp .

Docker compose example:

version: "3"

services:
  site:
    image: site:latest
    depends_on:
      - smtp
    links:
      - smtp
    volumes:
      - /etc/localtime:/etc/localtime:ro
    restart: unless-stopped
  smtp:
    image: smtp:latest
    environment:
      MAILNAME: "site"
      RELAY_NETWORKS: ":10.0.0.0/16" # Recieve smtp connections only from local network between containers 
    volumes:
      - /etc/localtime:/etc/localtime:ro
    restart: unless-stopped

Usage example in golang:

package main

import (
	"bytes"
	"log"
	"net/smtp"
)

func main() {
	
	// Connect to the remote SMTP server.
	c, err := smtp.Dial("smtp:25")
	if err != nil {
		log.Fatal(err)
	}
	defer c.Close()
	
	// Set the sender and recipient.
	c.Mail("sender@example.org")
	c.Rcpt("recipient@example.net")
	
	// Send the email body.
	wc, err := c.Data()
	if err != nil {
		log.Fatal(err)
	}
	defer wc.Close()
	buf := bytes.NewBufferString("This is the email body.")
	if _, err = buf.WriteTo(wc); err != nil {
		log.Fatal(err)
	}
}

Source

Based on https://github.com/namshi/docker-smtp

romainf / smtp