net/smtp: SendMail blocked at smtp.Client.StartTLS

[hiroyukki]

Go version

go version go1.20.13 windows/386

Output of go env in your module/workspace:

set GO111MODULE=
set GOARCH=386
set GOBIN=
set GOCACHE=C:\Users\jiayi\AppData\Local\go-build
set GOENV=C:\Users\jiayi\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=386
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=D:\gopath\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=D:\gopath
set GOPRIVATE=
set GOPROXY=https://goproxy.io
set GOROOT=D:\Programs\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=D:\Programs\go\pkg\tool\windows_386
set GOVCS=
set GOVERSION=go1.20.13
set GCCGO=gccgo
set GO386=sse2
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=E:\libgx\go\go.mod
set GOWORK=
set CGO_CFLAGS=-O2 -g
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS=-O2 -g
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m32 -mthreads -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=C:\Users\jiayi\AppData\Local\Temp\go-build1503534736=/tmp/go-build -gno-record-gcc-switches

What did you do?

I send mail with net/smtp, some smtp server seems incompatible, my code:

func main() {
from := "[email protected]"
to := []string{"[email protected]"}
auth := smtp.PlainAuth("", from, "wrong_pswd", "smtp.exmail.qq.com:25")
fmt.Println("pre sendMail")
fmt.Println(smtp.SendMail("smtp.exmail.qq.com:25", auth, from, to, []byte("hello")))
fmt.Println("post sendMail")
}

What did you see happen?

smtp.SendMail blocked (at smtp.Client.StartTLS) for about 2 minutes, until socket timeout

What did you expect to see?

STMP protocol can be run normally, failed or succeeded faithfully but not hang

[mknyszek]

This may be a long-shot but CC @bradfitz via https://dev.golang.org/owners. Maybe also CC @neild? Not sure.

[gabyhelp]

Similar Issues

• net/smtp: NewClient should initialize tls based on the incoming connection type #22166
• Fails to connect to SMTP with STARTTLS protocol #13694
• SMTP authentication method(loginauth) #40817
• net/smtp: in smtp.go, c.cmd(501, "*") takes long for server to respond. #18094
• dev.boringcrypto: Unable to connect to a server using the tls.TLS_RSA_WITH_AES_256_CBC_SHA CipherSuite #44050

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[rsc]

This program works fine for me (prints StartTLS worked) using a cloud system that can dial port 25 (my home internet gets blocked by my ISP):

package main

import (
	"crypto/tls"
	"log"
	"net/smtp"
)

func main() {
	addr := "smtp.exmail.qq.com:25"
	println("dial...")
	c, err := smtp.Dial(addr)
	if err != nil {
		log.Fatal(err)
	}
	defer c.Close()
	println("extensions?...")
	if ok, _ := c.Extension("STARTTLS"); ok {
		println("starttls...")
		config := &tls.Config{ServerName: "smtp.exmail.qq.com"}
		if err = c.StartTLS(config); err != nil {
			log.Fatal(err)
		}
		log.Fatal("StartTLS worked")
	}
	log.Fatalf("no tls")
}

Does it work for you?

[gopherbot]

Timed out in state WaitingForInfo. Closing.

(I am just a bot, though. Please speak up if this is a mistake or you have the requested information.)

[hiroyukki]

This program works fine for me (prints StartTLS worked) using a cloud system that can dial port 25 (my home internet gets blocked by my ISP):

package main

import (
	"crypto/tls"
	"log"
	"net/smtp"
)

func main() {
	addr := "smtp.exmail.qq.com:25"
	println("dial...")
	c, err := smtp.Dial(addr)
	if err != nil {
		log.Fatal(err)
	}
	defer c.Close()
	println("extensions?...")
	if ok, _ := c.Extension("STARTTLS"); ok {
		println("starttls...")
		config := &tls.Config{ServerName: "smtp.exmail.qq.com"}
		if err = c.StartTLS(config); err != nil {
			log.Fatal(err)
		}
		log.Fatal("StartTLS worked")
	}
	log.Fatalf("no tls")
}

Does it work for you?

seems not work, pending on StartTLS until timeout