Golang - Gmail API 400 BadRequest Failed Precondition

I've been struggling against this error (googleapi: Error 400: Bad Request, failedPrecondition) for about 8 hours now. I've written a simple go program which reproduces the problem for me. Maybe someone familiar with the Google APIs can help me out.

The error is the same as the one mentioned here: https://stackoverflow.com/questions/29327846/gmail-rest-api-400-bad-request-failed-precondition. The only difference is that it is in Go. I've followed the steps but still no luck.

I've also updated my code based on https://stackoverflow.com/questions/25382821/how-to-send-email-through-gmail-go-sdk/25387678#25387678

Both questions were helpful but did not help resolve the latest issue. I have also set GOOGLE_APPLICATION_CREDENTIALS to my project's json.

package main

import (
	"encoding/base64"
	"fmt"
	"log"
	"net/mail"
	"strings"

	"golang.org/x/net/context"
	"golang.org/x/oauth2/google"

	gmail "google.golang.org/api/gmail/v1"
)

func main() {
	// Use oauth2.NoContext if there isn't a good context to pass in.
	ctx := context.TODO()

	client, err := google.DefaultClient(ctx, gmail.GmailSendScope)
	if err != nil {
		panic(err)
	}

	// create service
	svc, err := gmail.New(client)
	if err != nil {
		log.Fatalf("Unable to create Gmail service: %v", err)
	}

	if err := SendEmail(ctx, svc, <redacted>); err != nil {
		log.Fatalf("failed to send email: %v", err)
	}
}

func SendEmail(ctx context.Context, svc *gmail.Service, email string) error {
	from := mail.Address{"", "noreply@example.com"}

	header := make(map[string]string)
	header["From"] = from.String()
	header["To"] = email
	header["Subject"] = encodeRFC2047("Hello, Gmail!")
	header["MIME-Version"] = "1.0"
	header["Content-Type"] = "text/html; charset=\"utf-8\""
	header["Content-Transfer-Encoding"] = "base64"

	var msg string
	for k, v := range header {
		msg += fmt.Sprintf("%s: %s\r\n", k, v)
	}
	msg += "\r\n" + "Hello, Gmail!"

	gmsg := gmail.Message{
		Raw: encodeWeb64String([]byte(msg)),
	}

	_, err := svc.Users.Messages.Send("me", &gmsg).Do()
	return err
}

func encodeRFC2047(s string) string {
	// use mail's rfc2047 to encode any string
	addr := mail.Address{s, ""}
	return strings.Trim(addr.String(), " <>")
}

func encodeWeb64String(b []byte) string {

	s := base64.URLEncoding.EncodeToString(b)

	var i = len(s) - 1
	for s[i] == '=' {
		i--
	}

	return s[0 : i+1]
}

Running the code above should produce the following error:

2015/12/12 22:16:46 failed to send email: googleapi: Error 400: Bad Request, failedPrecondition

To send mail, you must specify a valid address for the From: header (https://support.google.com/mail/answer/22370). noreply@example.com is unlikely to be such an address given that example.com is a test-only domain per RFC 2606.