go-simplest-smtp.go

import (
	"crypto/tls"
	"encoding/base64"
	"fmt"
	"log"
	"net"
	"net/smtp"
	"strings"
)

func SendMail(addr string, a smtp.Auth, from string, to []string, cc []string, bcc []string, subject string, msg []byte, use_tls bool) error {
	if use_tls {
		conn, err := tls.Dial("tcp", addr, nil)
		if err != nil {
			log.Println("Dialing Error:", err)
			return err
		}
		//分解主机端口字符串
		host, _, _ := net.SplitHostPort(addr)
		c, err := smtp.NewClient(conn, host)
		if err != nil {
			log.Println("SMTP New client Error:", err)
			return err
		}
		defer c.Close()

		if a != nil {
			if ok, _ := c.Extension("AUTH"); ok {
				if err = c.Auth(a); err != nil {
					fmt.Println("check auth with err:", err)
					return err
				}
			}
		}

		if err = c.Mail(from); err != nil {
			return err
		}
		for _, addr := range to {
			if err = c.Rcpt(addr); err != nil {
				return err
			}
		}
		w, err := c.Data()
		if err != nil {
			return err
		}

		header := make(map[string]string)
		header["Subject"] = subject
		header["MIME-Version"] = "1.0"
		header["Content-Type"] = "text/plain; charset=\"utf-8\""
		header["Content-Transfer-Encoding"] = "base64"
		header["From"] = from
		header["To"] = strings.Join(to, ";")
		header["CC"] = strings.Join(cc, ";")
		message := ""
		for k, v := range header {
			message += fmt.Sprintf("%s: %s\r\n", k, v)
		}
		message += "\r\n" + base64.StdEncoding.EncodeToString(msg)
		_, err = w.Write([]byte(message))

		if err != nil {
			return err
		}
		err = w.Close()
		if err != nil {
			return err
		}
		return c.Quit()
	} else {
		// host, port, _ := net.SplitHostPort(addr)
		err := smtp.SendMail(
			addr,
			a,
			from,
			to,
			[]byte(msg),
		)
		return err
	}
}