mailing

A Golang package for sending emails using SMTP, SparkPost, SendGrid and MailGun

This project starts from a full copy from https://github.com/harranali/mailing. 22 Sep 2026.

Features

• Multiple File attachments
• Multiple recipients
• Multiple CC
• Multiple BCC
• HTML content type support
• Plain Text content type support
• Easy integration with smtp4dev testing server for development
• Multiple Drivers Support: SMTP, SparkPost, SendGrid and MailGun

Install

Here is how to add it to your project

go get github.com/harranali/mailing

Using specific driver

// initiating the mailer with smtp driver
mailer := mailing.NewMailerWithSMTP(&mailing.SMTPConfig{
		Host:     "localhost", //the SMTP server host
		Port:     25, // The Port
		Username: "", 
		Password: "",
		TLSConfig: tls.Config{
			ServerName:         "localhost",
			InsecureSkipVerify: true, // (use true for development only) true accepts any certificate presented by the server
		},
	})

By default the driver selects the authentication mechanism dynamically: after STARTTLS it reads the server's advertised AUTH capabilities and prefers AUTH LOGIN (accepted by Microsoft Outlook/Office 365, Gmail, Amazon SES, Mailgun, SendGrid, Postmark, ...), falling back to AUTH PLAIN for legacy servers that only support it. This means Outlook/Office 365 accounts work out of the box even though they reject AUTH PLAIN.

You can force a specific mechanism through the AuthMechanism field:

mailer := mailing.NewMailerWithSMTP(&mailing.SMTPConfig{
		Host:          "smtp.office365.com",
		Port:          587,
		Username:      "user@yourdomain.com",
		Password:      "your-password",
		AuthMechanism: mailing.AuthLogin, // AuthAuto (default) | AuthLogin | AuthPlain
		TLSConfig: tls.Config{
			ServerName: "smtp.office365.com",
		},
	})

Leaving AuthMechanism empty keeps the previous behavior of being fully automatic and is backward compatible with existing configurations. AuthXOAuth2 is reserved as groundwork for OAuth2.

// initiating the mailer with SparkPost driver
mailer := mailing.NewMailerWithSparkPost(&mailing.SparkPostConfig{
		BaseUrl:    "https://api.sparkpost.com",
		ApiKey:     "test-api-key",
		ApiVersion: 1,
	})

// initiating the mailer with SendGrid driver
mailer := mailing.NewMailerWithSendGrid(&mailing.SendGridConfig{
		Host:     "https://api.sendgrid.com",
		Endpoint: "/v3/mail/send",
		ApiKey:   "API-KEY-HERE",
	})

// initiating the mailer with MailGun driver
mailer := mailing.NewMailerWithMailGun(&mailing.MailGunConfig{
		Domain: "your-domain.com",    // your-domain.com
		APIKey: "TEST-API-KEY", // your api key
		SkipTLSVerification true  // (set true for development only!) // true means accepts any tls certificate sent by the domain without verification
	})

Usage

Here is how to use it

// Initiate the package with SMTP Driver
mailer := mailing.NewMailerWithSMTP(&mailing.SMTPConfig{
		Host:     "localhost", //the SMTP server host
		Port:     25, // The Port
		Username: "", 
		Password: "",
		TLSConfig: tls.Config{
			ServerName:         "localhost",
			InsecureSkipVerify: true, // (use true for development only) true accepts any certificate presented by the server
		},
	})

// Set the Sender email address
mailer.SetFrom(mailing.EmailAddress{
        Name: "from name", // name can be set to empty string ("")
        Address: "from@mail.com",
    })

// Set the Recipients email addresses
mailer.SetTo([]mailing.EmailAddress{
        // name can be set to empty string ("")
        {Name: "first to name", Address: "theFirstTo@mail.com"},
        {Name: "second to name", Address: "theSecondTo@mail.com"},
    })

// Set CC email addresses
mailer.SetCC([]mailing.EmailAddress{
        // name can be set to empty string ("")
        {Name: "cc name", Address: "cc1@mail.com"},
        {Name: "cc name", Address: "cc2@mail.com"},
    })

// Set BCC email addresses
mailer.SetBCC([]mailing.EmailAddress{
        // name can be set to empty string ("")
        {Name: "bcc name", Address: "bcc@mail.com"},
    })

// Set the subject
mailer.SetSubject("This is the subject")

// Set the body (pick one: either HTML or Plain Text)
mailer.SetHTMLBody("<h1>This is the email body</h1>")
// OR
mailer.SetPlainTextBody("This is the email body")

// Set the sttachments files
mailer.SetAttachments([]mailing.Attachment{
        {
            Name: "first file",
            Path: "./myfiles/first-file.jpg",
        },
        {
            Name: "second file",
            Path: "./myfiles/second-file.pdf",
        },
    })
        
// Send the email
err := mailer.Send()
if err != nil {
    panic(err.Error())
}

Testing you emails with smtp4dev SMTP Testing Server

While developing your app you might need to test your emails, for that a customized docker-compose.yaml from the SMTP testing server smtp4dev is included.

Running the testing server

Copy the docker-compose.yaml to your pc, then start the container by running

docker-compose up

The testing server configuration

Here is how to connect to the testing server

mailer := mailing.NewMailerWithSMTP(&mailing.SMTPConfig{
		Host:     "localhost", //the SMTP server host
		Port:     25, // The Port
		Username: "", 
		Password: "",
		TLSConfig: tls.Config{
			ServerName:         "localhost",
			InsecureSkipVerify: true, // (use true for development only) true accepts any certificate presented by the server
		},
	})

Accessing the testing server UI

The testing server UI allows you to check the emails, here is a link to the ui of the testing server

http://localhost:5000