package main import (     "fmt"     "net/mail"     "net/smtp"     "encoding/base64" ) func main() {     b64 := base64.NewEncoding("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")     host := "smtp.mail.com"     email := "mail1@mail.com"     password := "password"     toEmail := "mail2@mail.com"     from := mail.Address{"发送人", email}     to := mail.Address{"接收人", toEmail}     header := make(map[string]string)     header["From"] = from.String()     header["To"] = to.String()     header["Subject"] = fmt.Sprintf("=?UTF-8?B?%s?=", b64.EncodeToString([]byte("邮件标题2")))     header["MIME-Version"] = "1.0"     header["Content-Type"] = "text/html; charset=UTF-8"     header["Content-Transfer-Encoding"] = "base64"     body := "我是一封电子邮件!golang发出.";     message := ""     for k, v := range header {         message += fmt.Sprintf("%s: %s\r\n", k, v)     }     message += "\r\n" + b64.EncodeToString([]byte(body))     auth := smtp.PlainAuth(         "",         email,         password,         host,     )     err := smtp.SendMail(         host+":25",         auth,         email,         []string{to.Address},         []byte(message),     )     if err != nil {         panic(err)     } }