Go, Appengine, SMTP, Gmail

Question

For some reason I cannot figure out how to send emails using a gmail account, Appengine and Golang.

Here's what I've done:

I went to Google Cloud Platform > Appengine > Settings > Select Project and I added the gmail account on Email API authorized senders.

I' tried to make this work using the code from (https://golang.org/pkg/net/smtp/#pkg-examples) (func SendMail)

package main

import (

    "log"
    "net/smtp"
)

func main() {

    // Set up authentication information.
    auth := smtp.PlainAuth("", "[email protected]", "password", "smtp.gmail.com")

    // Connect to the server, authenticate, set the sender and recipient,
    // and send the email all in one step.
    to := []string{"[email protected]"}
    msg := []byte("To: [email protected]\r\n" +
        "Subject: discount Gophers!\r\n" +
        "\r\n" +
        "This is the email body.\r\n")
    err := smtp.SendMail(smtp.gmail.com:587", auth, "[email protected]", to, msg)
    if err != nil {
        log.Fatal(err)
    }
}

On the front-end (JavaScript) I get an unsuccessful response after trying to run this code.

I've been running this on the appengine staging server

I tried different smtp server, ports, users and it still not work (support.google.com/a/answer/176600?hl=en)

I found a few examples on github and some other blog and I tried them but it didn't make different. github.com/golang/go/wiki/SendingMail

nathanleclaire.com/blog/2013/12/17/sending-email-from-gmail-using-golang/

On all the examples it everything looks straight forward but there's something that I'm definitely missing or misunderstanding.

FYI: I've just successfully sent an email with your code using my gmail account. — oharlem
Did you use the code locally or on Google Appengine. There are few things that work slightly different on App engine. — Moisés Colón Ponce
locally. hm... then my only guess is ports. Will telnet smtp.gmail.com 587 work from your instance? — oharlem
I tried it but it won't telnet smtp.gmail.com 587 from the appengine container. I know that there's a gmail api on Google Cloud Platform but I was hoping to send email in a simple way using smtp before trying to there. — Moisés Colón Ponce
Yeah, that's what I thought. Additionally, I see that app engine does not allow standard ports (cloud.google.com/compute/docs/tutorials/sending-mail ). — oharlem

Marius Marius · Accepted Answer · 2016-12-09T05:43:20

There're some limitations with establishing raw tcp connections on GAE: https://cloud.google.com/appengine/docs/go/sockets/#limitations_and_restrictions

I would recommend to use GAE mail api (which is slightly diffrent from standart smtp package) to send emails: https://cloud.google.com/appengine/docs/go/mail/sending-receiving-with-mail-api

Go, Appengine, SMTP, Gmail

1 Answers