add chapter 15.12 (#689)

eBook/examples/chapter_15/smtp.go

@@ -0,0 +1,30 @@
+// smtp.go
+package main
+
+import (
+        "bytes"
+        "log"
+        "net/smtp"
+)
+
+func main() {
+        // Connect to the remote SMTP server.
+        client, err := smtp.Dial("mail.example.com:25")
+        if err != nil {
+                log.Fatal(err)
+        }
+        // Set the sender and recipient.
+        client.Mail("sender@example.org")
+        client.Rcpt("recipient@example.net")
+        // Send the email body.
+        wc, err := client.Data()
+        if err != nil {
+                log.Fatal(err)
+        }
+        defer wc.Close()
+        buf := bytes.NewBufferString("This is the email body.")
+        if _, err = buf.WriteTo(wc); err != nil {
+                log.Fatal(err)
+        }
+}
+

eBook/examples/chapter_15/smtp_auth.go

@@ -0,0 +1,29 @@
+// smtp_auth.go
+package main
+
+import (
+        "log"
+        "net/smtp"
+)
+
+func main() {
+        // Set up authentication information.
+        auth := smtp.PlainAuth(
+                "",
+                "user@example.com",
+                "password",
+                "mail.example.com",
+        )
+        // Connect to the server, authenticate, set the sender and recipient,
+        // and send the email all in one step.
+        err := smtp.SendMail(
+                "mail.example.com:25",
+                auth,
+                "sender@example.org",
+                []string{"recipient@example.net"},
+                []byte("This is the email body."),
+        )
+        if err != nil {
+                log.Fatal(err)
+        }
+}