Di Valyent, kami sedang membina perisian sumber terbuka untuk pembangun.
Sebagai sebahagian daripada misi ini, kami sedang membangunkan Ferdinand, perkhidmatan penghantaran e-mel kami untuk pembangun (kini dalam alfa).
Infrastruktur e-mel bergantung pada beberapa protokol utama, dengan yang paling penting ialah:
Dalam artikel hari ini, kami akan menumpukan pada membina pelayan SMTP keluar kami sendiri, mencerminkan pendekatan yang telah kami ambil dengan Ferdinand. Dengan berbuat demikian, kami akan mendapat pemahaman yang mendalam tentang komponen paling penting dalam infrastruktur penghantaran e-mel.
"Apa yang saya tidak boleh cipta, saya tidak faham."
— Richard Feynman
Dengan membina pelayan SMTP keluar dari awal, anda boleh memperoleh tahap cerapan tentang penghantaran e-mel yang tidak pernah dicapai oleh kebanyakan pembangun.
Untuk meneruskan, kami akan menggunakan bahasa pengaturcaraan Go, bersama-sama dengan perpustakaan mel hebat daripada Simon Ser. Kami akan mentafsirkan proses itu, menunjukkan kepada anda cara menghantar e-mel ke pelayan lain dan juga menerangkan konsep utama seperti SPF, DKIM dan DMARC yang membenarkan kebolehhantaran.
Pada akhirnya, anda akan mempunyai sekurang-kurangnya pemahaman yang lebih mendalam tentang infrastruktur e-mel, walaupun tidak mempunyai pelayan SMTP sedia pengeluaran.
Sebelum kita menyelami kod, mari semak apa itu SMTP dan cara ia berfungsi. SMTP (Simple Mail Transfer Protocol) ialah protokol standard untuk menghantar e-mel merentasi Internet. Ia adalah protokol berasaskan teks yang agak mudah yang beroperasi pada model pelayan pelanggan.
Protokol SMTP menggunakan arahan. Setiap arahan dalam SMTP mempunyai tujuan tertentu dalam proses penghantaran e-mel. Mereka membenarkan pelayan memperkenalkan diri mereka, menentukan penghantar dan penerima, memindahkan kandungan e-mel sebenar dan mengurus sesi komunikasi keseluruhan. Fikirkan arahan ini sebagai perbualan berstruktur antara dua pelayan e-mel, dengan setiap perintah mewakili pernyataan atau soalan tertentu dalam perbualan itu.
Apabila anda membina pelayan SMTP, anda pada asasnya mencipta program yang boleh bercakap bahasa ini dengan lancar, mentafsir arahan masuk dan bertindak balas dengan sewajarnya, serta mengeluarkan arahan yang betul semasa menghantar e-mel.
Mari terokai arahan SMTP yang paling penting untuk melihat bagaimana perbualan ini berlaku:
DATA From: john@example.com To: jane@example.com Subject: Hello This is the body of the email. .
Perbualan SMTP biasa mungkin kelihatan seperti ini:
C: EHLO client.example.com S: 250-smtp.example.com Hello client.example.com S: 250-SIZE 14680064 S: 250-AUTH LOGIN PLAIN S: 250 HELP C: MAIL FROM:<sender@example.com> S: 250 OK C: RCPT TO:<recipient@example.com> S: 250 OK C: DATA S: 354 Start mail input; end with <CRLF>.<CRLF> C: From: sender@example.com C: To: recipient@example.com C: Subject: Test Email C: C: This is a test email. C: . S: 250 OK: queued as 12345 C: QUIT S: 221 Bye
Pengesahan ialah aspek penting SMTP, terutamanya untuk pelayan e-mel keluar. Ia membantu menghalang penggunaan pelayan tanpa kebenaran dan mengurangkan spam. Terdapat beberapa kaedah pengesahan yang digunakan dalam SMTP:
Here's an example of how PLAIN authentication looks in an SMTP conversation:
C: EHLO example.com S: 250-STARTTLS S: 250 AUTH PLAIN LOGIN C: AUTH PLAIN AGVtYWlsQGV4YW1wbGUuY29tAHBhc3N3b3Jk S: 235 2.7.0 Authentication successful
In this example, AGVtYWlsQGV4YW1wbGUuY29tAHBhc3N3b3Jk is the base64-encoded version of \0email@example.com\0password.
When implementing authentication in your SMTP server, you'll need to:
Now, let's move on to implementing these concepts in our Go SMTP server.
Imagine sending a letter through the postal service without a return address or an official stamp. It might reach its destination, but there's a good chance it'll end up in the "suspicious mail" pile. In the digital world of email, we face a similar challenge.
How do we ensure our emails aren't just sent, but actually delivered and trusted?
Enter the holy trinity of email authentication: DKIM, SPF, and DMARC.
DKIM (DomainKeys Identified Mail) is like a wax seal on a medieval letter. It proves the email hasn't been tampered with during transit.
How it works:
Think of it as your email's passport, stamped and verified at each checkpoint.
Example DKIM DNS Record:
<selector>._domainkey.<domain>.<tld>. IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC3QEKyU1fSma0axspqYK5iAj+54lsAg4qRRCnpKK68hawSd8zpsDz77ntGCR0X2mHVvkHbX6dX...oIDAQAB"
Here, 'selector' is a unique identifier for this DKIM key, and the long string is your public key.
SPF (Sender Policy Framework) is like the bouncer at an exclusive club. It specifies which email servers are allowed to send emails on behalf of your domain.
How it works:
It's like saying, "If the email didn't come from one of these guys, it's not with us!"
Example SPF DNS Record:
<domain>.<tld>. IN TXT "v=spf1 ip4:192.0.2.0/24 include:_spf.google.com ~all"
This record says:
DMARC (Domain-based Message Authentication, Reporting & Conformance) is the wise judge that decides what happens to emails that fail DKIM or SPF checks.
How it works:
Think of DMARC as your email bouncer's rulebook and incident report.
Example DMARC DNS Record:
_dmarc.<domain>.<tld>. IN TXT "v=DMARC1; p=quarantine; rua=mailto:dmarc-reports@<domain>.<tld>"
This record says:
Together, DKIM, SPF, and DMARC form a powerful shield against email spoofing and phishing. They tell receiving servers, "This email is really from us, sent by someone we trust, and here's what to do if something seems fishy."
Implementing this trinity not only improves your email deliverability but also protects your domain's reputation. It's like having a state-of-the-art security system for your email infrastructure.
As we build our SMTP server, keeping these authentication methods in mind will be crucial for ensuring our emails don't just get sent, but actually reach their destination and are trusted when they arrive. Remember, when implementing these records on a production domain, start with permissive policies and gradually tighten them as you confirm everything is working correctly.
First, let's create a new directory for our project and initialize a Go module:
mkdir go-smtp-server cd go-smtp-server go mod init github.com/yourusername/go-smtp-server
We'll need a few dependencies for our SMTP server. Run the following commands:
go get github.com/emersion/go-smtp go get github.com/emersion/go-sasl go get github.com/emersion/go-msgauth
package main
import (
"log"
"time"
"io"
"github.com/emersion/go-smtp"
)
func main() {
s := smtp.NewServer(&Backend{})
s.Addr = ":2525"
s.Domain = "localhost"
s.WriteTimeout = 10 * time.Second
s.ReadTimeout = 10 * time.Second
s.MaxMessageBytes = 1024 * 1024
s.MaxRecipients = 50
s.AllowInsecureAuth = true
log.Println("Starting server at", s.Addr)
if err := s.ListenAndServe(); err != nil {
log.Fatal(err)
}
}
// Backend implements SMTP server methods.
type Backend struct{}
func (bkd *Backend) NewSession(_ *smtp.Conn) (smtp.Session, error) {
return &Session{}, nil
}
// A Session is returned after EHLO.
type Session struct{}
// We'll implement the Session methods next
This creates an SMTP server, listening on the 2525 port, a convenient choice for development purposes, since this port doesn’t require administrative privileges, unlike the standard ports 25 (standard SMTP), 465 (TLS), 587 (STARTTLS).
The EHLO/HELO command is handled automatically by the go-smtp library. We don't need to implement it ourselves.
Add this method to the Session struct:
func (s *Session) Mail(from string, opts *smtp.MailOptions) error {
fmt.Println("Mail from:", from) s.From = from
return nil
}
This method is called when the server receives a MAIL FROM command. It logs the sender's address and stores it in the session.
Add this method to the Session struct:
func (s *Session) Rcpt(to string) error {
fmt.Println("Rcpt to:", to)
s.To = append(s.To, to)
return nil
}
This method is called for each RCPT TO command. It logs the recipient's address and adds it to the list of recipients for this session.
Add this method to the Session struct:
import (
"fmt"
"io"
)
func (s *Session) Data(r io.Reader) error {
if b, err := io.ReadAll(r); err != nil {
return err
} else {
fmt.Println("Received message:", string(b))
// Here you would typically process the email
return nil
}
}
This method is called when the server receives the DATA command. It reads the entire email message and logs it. In a real server, you would process the email here.
Add this method to the Session struct:
func (s *Session) AuthPlain(username, password string) error {
if username != "testuser" || password != "testpass" {
return fmt.Errorf("Invalid username or password")
}
return nil
}
This implements a basic authentication mechanism. Note that this is for demonstration purposes only and should not be used in production.
Add this method to the Session struct:
func (s *Session) Reset() {
s.From = "" s.To = []string{}
}
This method is called when the server receives a RSET command. It resets the session state.
Add this method to the Session struct:
func (s *Session) Logout() error {
return nil
}
This method is called when the server receives a QUIT command. In this simple implementation, we don't need to do anything special.
Once we've received and processed an email, the next step is to send it to its destination. This involves two key steps: finding the recipient's mail server using MX (Mail Exchanger) records, and attempting to send the email using standard SMTP ports.
First, let's add a function to look up MX records:
import "net"
func lookupMX(domain string) ([]*net.MX, error) {
mxRecords, err := net.LookupMX(domain)
if err != nil {
return nil, fmt.Errorf("Error looking up MX records: %v", err)
}
return mxRecords, nil
}
Next, let's create a function that attempts to send an email using different ports:
import (
"crypto/tls"
"net/smtp"
"strings"
)
func sendMail(from string, to string, data []byte) error {
domain := strings.Split(to, "@")[1]
mxRecords, err := lookupMX(domain)
if err != nil {
return err
}
for _, mx := range mxRecords {
host := mx.Host
for _, port := range []int{25, 587, 465} {
address := fmt.Sprintf("%s:%d", host, port)
var c *smtp.Client
var err error
switch port {
case 465:
// SMTPS
tlsConfig := &tls.Config{ServerName: host}
conn, err := tls.Dial("tcp", address, tlsConfig)
if err != nil {
continue
}
c, err = smtp.NewClient(conn, host)
case 25, 587:
// SMTP or SMTP with STARTTLS
c, err = smtp.Dial(address)
if err != nil {
continue
}
if port == 587 {
if err = c.StartTLS(&tls.Config{ServerName: host}); err != nil {
c.Close()
continue
}
}
}
if err != nil {
continue
}
// SMTP conversation
if err = c.Mail(from); err != nil {
c.Close()
continue
}
if err = c.Rcpt(to); err != nil {
c.Close()
continue
}
w, err := c.Data()
if err != nil {
c.Close()
continue
}
if _, err := w.Write(data); err != nil {
c.Close()
continue
}
err = w.Close()
if err != nil {
c.Close()
continue
}
c.Quit()
return nil
}
}
return fmt.Errorf("Failed to send email to %s", to)
}
This function does the following:
Now, let's modify our Data method in the Session struct to use this new sendMail function:
func (s *Session) Data(r io.Reader) error {
if data, err := io.ReadAll(r); err != nil {
return err
} else {
fmt.Println("Received message:", string(data))
for _, recipient := range s.To {
if err := sendMail(s.From, recipient, data); err != nil {
fmt.Printf("Failed to send email to %s: %v", recipient, err)
} else {
fmt.Printf("Email sent successfully to %s", recipient)
}
}
return nil
}
}
This implementation will attempt to send the received email to each recipient using the appropriate mail server and port.
Now, let's add DKIM signing to our email sending process. First, we need to import the necessary packages and set up our DKIM options:
import (
// ... other imports ...
"crypto/rsa"
"crypto/x509"
"encoding/pem"
"github.com/emersion/go-msgauth/dkim"
)
// Load your DKIM private key
var dkimPrivateKey *rsa.PrivateKey
func init() {
// Load your DKIM private key from a file
privateKeyPEM, err := ioutil.ReadFile("path/to/your/private_key.pem")
if err != nil {
log.Fatalf("Failed to read private key: %v", err)
}
block, _ := pem.Decode(privateKeyPEM)
if block == nil {
log.Fatalf("Failed to parse PEM block containing the private key")
}
privateKey, err := x509.ParsePKCS1PrivateKey(block.Bytes)
if err != nil {
log.Fatalf("Failed to parse private key: %v", err)
}
dkimPrivateKey = privateKey
}
// DKIM options
var dkimOptions = &dkim.SignOptions{
Domain: "example.com",
Selector: "default",
Signer: dkimPrivateKey,
}
Next, let's modify our sendMail function to include DKIM signing:
func sendMail(from string, to string, data []byte) error {
// ... [previous MX lookup code] ...
for _, mx := range mxRecords {
host := mx.Host
for _, port := range []int{25, 587, 465} {
// ... [previous connection code] ...
// DKIM sign the message
var b bytes.Buffer
if err := dkim.Sign(&b, bytes.NewReader(data), dkimOptions); err != nil {
return fmt.Errorf("Failed to sign email with DKIM: %v", err)
}
signedData := b.Bytes()
// SMTP conversation
if err = c.Mail(from); err != nil {
c.Close()
continue
}
if err = c.Rcpt(to); err != nil {
c.Close()
continue
}
w, err := c.Data()
if err != nil {
c.Close()
continue
}
_, err = w.Write(signedData) // Use the DKIM signed message
if err != nil {
c.Close()
continue
}
err = w.Close()
if err != nil {
c.Close()
continue
}
c.Quit()
return nil
}
}
return fmt.Errorf("Failed to send email to %s", to)
}
In this updated sendMail function:
This implementation will add a DKIM signature to your outgoing emails, which will help improve deliverability and authenticity of your emails.
Ingat untuk menggantikan "path/to/your/private_key.pem" dengan laluan sebenar ke kunci peribadi DKIM anda dan kemas kini Domain dan Pemilih dalam dkimOptions untuk memadankan rekod DNS DKIM anda.
Walaupun pelaksanaan ini menyediakan pelayan SMTP berfungsi asas yang mampu menerima dan menghantar e-mel, terdapat beberapa pertimbangan penting untuk pelayan sedia pengeluaran:
Kami harap anda belajar banyak dengan membaca siaran ini. Untuk mengetahui lebih lanjut tentang menghantar e-mel, sila lihat repositori GitHub Ferdinand dan terokai kod tersebut.
Atas ialah kandungan terperinci Bina Pelayan SMTP Anda Sendiri dalam Go. Untuk maklumat lanjut, sila ikut artikel berkaitan lain di laman web China PHP!
Mengapa wifi mempunyai tanda seru?
Cara mengalih keluar tera air TikTok orang lain daripada video TikTok
Trend harga terkini Bitcoin
10 pertukaran mata wang digital paling selamat pada tahun 2024
Mengapa webstorm tidak boleh menjalankan fail
Cara menggunakan busybox
Bagaimana untuk memulihkan data selepas pemformatan
Apakah alamat laman sesawang Ouyi?
![[Web front-end] Permulaan pantas Node.js](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
