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@douglasmakey douglasmakey/sender.go
Last active Aug 30, 2019

What would you like to do?
Golang - send an email with attachments.
package main
import (
var (
host = os.Getenv("EMAIL_HOST")
username = os.Getenv("EMAiL_USERNAME")
password = os.Getenv("EMAIL_PASSWORD")
portNumber = os.Getenv("EMAIL_PORT")
type Sender struct {
auth smtp.Auth
type Message struct {
To []string
Subject string
Body string
Attachments map[string][]byte
func New() *Sender {
auth := smtp.PlainAuth("", username, password, host)
return &Sender{auth}
func (s *Sender) Send(m *Message) error {
return smtp.SendMail(fmt.Sprintf("%s:%s", host, portNumber), s.auth, username, m.To, m.ToBytes())
func NewMessage(s, b string) *Message {
return &Message{Subject: s, Body: b, Attachments: make(map[string][]byte)}
func (m *Message) AttachFile(src string) error {
b, err := ioutil.ReadFile(src)
if err != nil {
return err
_, fileName := filepath.Split(src)
m.Attachments[fileName] = b
return nil
func (m *Message) ToBytes() []byte {
buf := bytes.NewBuffer(nil)
withAttachments := len(m.Attachments) > 0
buf.WriteString(fmt.Sprintf("Subject: %s\n", m.Subject))
buf.WriteString("MIME-Version: 1.0\n")
writer := multipart.NewWriter(buf)
boundary := writer.Boundary()
if withAttachments {
buf.WriteString(fmt.Sprintf("Content-Type: multipart/mixed; boundary=%s\n", boundary))
buf.WriteString(fmt.Sprintf("--%s\n", boundary))
buf.WriteString("Content-Type: text/plain; charset=utf-8\n")
if withAttachments {
for k, v := range m.Attachments {
buf.WriteString(fmt.Sprintf("\n\n--%s\n", boundary))
buf.WriteString("Content-Type: application/octet-stream\n")
buf.WriteString("Content-Transfer-Encoding: base64\n")
buf.WriteString(fmt.Sprintf("Content-Disposition: attachment; filename=%s\n", k))
b := make([]byte, base64.StdEncoding.EncodedLen(len(v)))
base64.StdEncoding.Encode(b, v)
buf.WriteString(fmt.Sprintf("\n--%s", boundary))
return buf.Bytes()
func main() {
sender := New()
m := NewMessage("Test", "Body message.")
m.To = []string{""}
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