SMIME Signing Example

This example shows how to enable S/MIME signing in go-mail.

Test on play.go.dev

package main

import (
	"crypto/tls"
	"log"
	"os"

	"github.com/wneessen/go-mail"
)

func main() {
	// Load the TLS certificate from the certificate and key file
	keypair, err := tls.LoadX509KeyPair("cert.pem", "key.pem")
	if err != nil {
		log.Fatalf("failed to load keypair: %s", err)
	}

	message := mail.NewMsg()
	if err = message.From("[email protected]"); err != nil {
		log.Fatalf("failed to set FROM address: %s", err)
	}
	if err = message.To("[email protected]"); err != nil {
		log.Fatalf("failed to set TO address: %s", err)
	}
	message.Subject("This is my first test mail with go-mail!")
	message.SetBodyString(mail.TypeTextPlain, "This will be the content of the mail.")
	
	// Initialize the S/MIME signing
	if err = message.SignWithTLSCertificate(&keypair); err != nil {
		log.Fatalf("failed to sign message: %s", err)
	}

	// Deliver the mails via SMTP
	client, err := mail.NewClient(os.Getenv("SMTP_HOST"),
		mail.WithSMTPAuth(mail.SMTPAuthAutoDiscover), mail.WithTLSPortPolicy(mail.TLSMandatory),
		mail.WithUsername(os.Getenv("SMTP_USER")), mail.WithPassword(os.Getenv("SMTP_PASS")),
	)
	if err != nil {
		log.Fatalf("failed to create new mail delivery client: %s", err)
	}
	if err := client.DialAndSend(message); err != nil {
		log.Fatalf("failed to deliver mail: %s", err)
	}
	log.Printf("Test mail successfully delivered.")
}

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

The main differences to the Simple Mailer Example are, that we load our TLS certificate from a X.509 RSA private-/public keypair in the first few lines of code. Later, when our message is composed, we initialize the S/MIME signing using the Msg.SignWithTLSCertifcate method and provide our imported keypair as parameter. This makes sure, once the mail is rendered during the delivery process, that the mail is S/MIME signed before it's sent out.