SOCKS5 Proxy Example

While go-mail by default does not implement SOCKS5 Proxy support, it provides support for custom DialContext functions. This can be used in combination with golang.org/x/net/proxy to implement a custom dial context with SOCKS5 support.

This example code shows how this could look like.

Test on play.go.dev

package main

import (
	"context"
	"log"
	"net"

	"github.com/wneessen/go-mail"
	"golang.org/x/net/proxy"
)

func main() {
	message := mail.NewMsg()
	if err := message.From("toni.sender@example.com"); err != nil {
		log.Fatalf("failed to set From address: %s", err)
	}
	if err := message.To("tina.recipient@example.com"); err != nil {
		log.Fatalf("failed to set To address: %s", err)
	}
	message.Subject("This is my first mail with go-mail!")
	message.SetBodyString(mail.TypeTextPlain, "Do you like this mail? I certainly do!")

	dialer, err := proxy.SOCKS5("tcp", "127.0.0.1:1080", nil, proxy.Direct)
	if err != nil {
		log.Fatalf("failed to create SOCKS5 proxy: %s", err)
	}
	client, err := mail.NewClient("smtp.example.com", mail.WithSMTPAuth(mail.SMTPAuthAutoDiscover),
		mail.WithUsername("my_username"), mail.WithPassword("extremely_secret_pass"),
		mail.WithDialContextFunc(func(_ context.Context, network, addr string) (net.Conn, error) {
			return dialer.Dial(network, addr)
		}),
	)
	if err != nil {
		log.Fatalf("failed to create mail client: %s", err)
	}
	if err := client.DialAndSend(message); err != nil {
		log.Fatalf("failed to send mail: %s", err)
	}
}

Most of the code is explained in the Simple-Mailer-Example. Check out that page for detailed explanations.

The only difference is, that before initializing the Client, we create a new SOCKS5 dialer using the golang.org/x/net/proxy package. This dial is then used in our custom DialContextFunc which we add to the client initialization using the mail.WithDialContextFunc option. Now, once the client tries to connect to the SMTP server, it will tunnel the traffic through the SOCKS5 proxy instead.