gomail: could not send email 1: 502 5.3.3 Command not implemented

[lvjianzhao]

When I use go 1.16, I get an error:

2025/02/26 19:10:27 邮件发送失败：gomail: could not send email 1: 502 5.3.3 Command not implemented
exit status 1

When I use go 1.15, I can send normally:

$ g use 1.15
go version go1.15 windows/amd64
$ go run main.go
邮件发送成功！

My code is as follows:

package main

import (
    "fmt"
    "gopkg.in/gomail.v2"
    "log"
    "crypto/tls"
)

func SendEmail() {
    // 邮件内容
    from := "[email protected]"  // 发件人邮箱
    password := "xxxxxxxxx" // 发件人邮箱密码
    to := "[email protected]" // 收件人邮箱
    subject := "邮件发送测试"
    body := "这是一个简单的邮件测试内容xxaaa！"

    // 创建邮件对象
    m := gomail.NewMessage()

    // 设置发件人、收件人和邮件主题
    m.SetHeader("From", from)
    m.SetHeader("To", to)
    m.SetHeader("Subject", subject)

    // 设置邮件内容
    m.SetBody("text/plain", body)

    // 创建SMTP客户端
    d := gomail.NewDialer("email.xxxx.com", 25, from, password)


    d.TLSConfig = &tls.Config{InsecureSkipVerify: true}

    // 发送邮件
    if err := d.DialAndSend(m); err != nil {
        log.Fatal("邮件发送失败：", err)
    } else {
        fmt.Println("邮件发送成功！")
    }
}

func main() {
    SendEmail()
}

What is the reason?

[wneessen]

That's hard to tell without seeing the communication between the client and the server. The client is sending something that the server does not like/supports. The only thing I can see that has been changed in net/smtp between v1.15 and v1.16 is the addition of SMTPUTF8 support but I do not think that this might cause the issue. In any case 1.15 and 1.16 are very old versions of Go. You might want to update to a newer version to not run into security vulnerabilities.

That being said, this package is not maintained anymore since the author sadly passed away. You can have a go with go-mail which supports debug logging. It can show you the communication between the client and the server, which might shed some light into what exactly the server doesn't like.

[lvjianzhao]

@wneessen Thank you for your reply. I will try go-mail later.