Golang StartTLS SMTP Example

starttls_smtp_example.go

package main

import (
    "fmt"
    "log"
    "net"
    "net/mail"
    "net/smtp"
    "crypto/tls"
)

// StartTLS Email Example

func main() {

    from := mail.Address{"", "[email protected]"}
    to   := mail.Address{"", "[email protected]"}
    subj := "This is the email subject"
    body := "This is an example body.\n With two lines."

    // Setup headers
    headers := make(map[string]string)
    headers["From"] = from.String()
    headers["To"] = to.String()
    headers["Subject"] = subj

    // Setup message
    message := ""
    for k,v := range headers {
        message += fmt.Sprintf("%s: %s\r\n", k, v)
    }
    message += "\r\n" + body

    // Connect to the SMTP Server
    servername := "smtp.example.tld:465"

    host, _, _ := net.SplitHostPort(servername)

    auth := smtp.PlainAuth("","[email protected]", "password", host)

    // TLS config
    tlsconfig := &tls.Config {
        InsecureSkipVerify: true,
        ServerName: host,
    }

    c, err := smtp.Dial(servername)
    if err != nil {
        log.Panic(err)
    }

    c.StartTLS(tlsconfig)

    // Auth
    if err = c.Auth(auth); err != nil {
        log.Panic(err)
    }

    // To && From
    if err = c.Mail(from.Address); err != nil {
        log.Panic(err)
    }

    if err = c.Rcpt(to.Address); err != nil {
        log.Panic(err)
    }

    // Data
    w, err := c.Data()
    if err != nil {
        log.Panic(err)
    }

    _, err = w.Write([]byte(message))
    if err != nil {
        log.Panic(err)
    }

    err = w.Close()
    if err != nil {
        log.Panic(err)
    }

    c.Quit()

}

I have try this example to send a mail via smtp.office365.com:587 and got error after c.Auth(), there is error message:

2024/12/02 15:50:16 504 5.7.4 Unrecognized authentication type [TPYP295CA0020.TWNP295.PROD.OUTLOOK.COM 2024-12-02T07:50:11.227Z 08DD11A71FE694FB]
panic: 504 5.7.4 Unrecognized authentication type [TPYP295CA0020.TWNP295.PROD.OUTLOOK.COM 2024-12-02T07:50:11.227Z 08DD11A71FE694FB]

does any one can give some suggestion?