feat: add function ValidateHostAndUser to validate host and user preventing SPAN and BOT

README.md

@@ -11,34 +11,42 @@
 
 ### 1. Format
 ```go
-    func main() {
-		err := checkmail.ValidateFormat("ç$€§/[email protected]")
-		if err != nil {
-			fmt.Println(err)
-		}
-	}
+func main() {
+    err := checkmail.ValidateFormat("ç$€§/[email protected]")
+    if err != nil {
+        fmt.Println(err)
+    }
+}
 ```
 output: `invalid format`
 
 ### 2. Domain
 ```go
-    func main() {
-		err := checkmail.ValidateHost("[email protected]")
-		if err != nil {
-			fmt.Println(err)
-		}
-	}
+func main() {
+    err := checkmail.ValidateHost("[email protected]")
+    if err != nil {
+        fmt.Println(err)
+    }
+}
 ```
 output: `unresolvable host`
 
-### 3. User
+### 3. Host and User
+
+If host is valid, requires valid SMTP `serverHostName` (see to [online validator](https://mxtoolbox.com/SuperTool.aspx)) and `serverMailAddress` to reverse validation 
+for prevent SPAN and BOTS.
+
 ```go
-    func main() {
-		err := checkmail.ValidateHost("[email protected]")
-		if smtpErr, ok := err.(checkmail.SmtpError); ok && err != nil {
-			fmt.Printf("Code: %s, Msg: %s", smtpErr.Code(), smtpErr)
-		}
-	}
+func main() {
+    var (
+        serverHostName    = "smtp.myserver.com" // set your SMTP server here
+        serverMailAddress = "[email protected]"  // set your valid mail address here
+    )
+    err := checkmail.ValidateHostAndUser(serverHostName, serverMailAddress, "[email protected]")
+    if smtpErr, ok := err.(checkmail.SmtpError); ok && err != nil {
+        fmt.Printf("Code: %s, Msg: %s", smtpErr.Code(), smtpErr)
+    }
+}
 ```
 output: `Code: 550, Msg: 550 5.1.1 The email account that you tried to reach does not exist.`
 

checkmail.go

@@ -37,31 +37,50 @@ var (
 	emailRegexp = regexp.MustCompile("^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$")
 )
 
+
 func ValidateFormat(email string) error {
 	if !emailRegexp.MatchString(email) {
 		return ErrBadFormat
 	}
 	return nil
 }
 
+// ValidateHost validate mail host.
 func ValidateHost(email string) error {
 	_, host := split(email)
 	mx, err := net.LookupMX(host)
 	if err != nil {
 		return ErrUnresolvableHost
 	}
+	client, err := DialTimeout(fmt.Sprintf("%s:%d", mx[0].Host, 25), forceDisconnectAfter)
+	if err != nil {
+		return NewSmtpError(err)
+	}
+	client.Close()
+	return nil
+}
 
+// ValidateHostAndUser validate mail host and user.
+// If host is valid, requires valid SMTP [1] serverHostName and serverMailAddress to reverse validation
+// for prevent SPAN and BOTS.
+// [1] https://mxtoolbox.com/SuperTool.aspx
+func ValidateHostAndUser(serverHostName, serverMailAddress, email string) error {
+	_, host := split(email)
+	mx, err := net.LookupMX(host)
+	if err != nil {
+		return ErrUnresolvableHost
+	}
 	client, err := DialTimeout(fmt.Sprintf("%s:%d", mx[0].Host, 25), forceDisconnectAfter)
 	if err != nil {
 		return NewSmtpError(err)
 	}
 	defer client.Close()
 
-	err = client.Hello("checkmail.me")
+	err = client.Hello(serverHostName)
 	if err != nil {
 		return NewSmtpError(err)
 	}
-	err = client.Mail("[email protected]")
+	err = client.Mail(serverMailAddress)
 	if err != nil {
 		return NewSmtpError(err)
 	}

checkmail_test.go

@@ -1,9 +1,10 @@
-package checkmail_test
+package checkmail
 
 import (
+	"fmt"
+	"os"
 	"testing"
 
-	"github.com/badoux/checkmail"
 )
 
 var (
@@ -35,7 +36,27 @@ func TestValidateHost(t *testing.T) {
 			continue
 		}
 
-		err := checkmail.ValidateHost(s.mail)
+		err := ValidateHost(s.mail)
+		if err != nil && s.account == true {
+			t.Errorf(`"%s" => unexpected error: "%v"`, s.mail, err)
+		}
+		if err == nil && s.account == false {
+			t.Errorf(`"%s" => expected error`, s.mail)
+		}
+	}
+}
+
+func TestValidateHostAndUser(t *testing.T) {
+	var (
+		serverHostName = getenv(t, "self_hostname")
+		serverMailAddress = getenv(t, "self_mail")
+	)
+	for _, s := range samples {
+		if !s.format {
+			continue
+		}
+
+		err := ValidateHostAndUser(serverHostName, serverMailAddress, s.mail)
 		if err != nil && s.account == true {
 			t.Errorf(`"%s" => unexpected error: "%v"`, s.mail, err)
 		}
@@ -47,7 +68,7 @@ func TestValidateHost(t *testing.T) {
 
 func TestValidateFormat(t *testing.T) {
 	for _, s := range samples {
-		err := checkmail.ValidateFormat(s.mail)
+		err := ValidateFormat(s.mail)
 		if err != nil && s.format == true {
 			t.Errorf(`"%s" => unexpected error: "%v"`, s.mail, err)
 		}
@@ -56,3 +77,11 @@ func TestValidateFormat(t *testing.T) {
 		}
 	}
 }
+
+func getenv(t *testing.T, name string) (value string) {
+	name = "test_checkmail_"+name
+	if value = os.Getenv(name); value =="" {
+		panic(fmt.Errorf("enviroment variable %q is not defined", name))
+	}
+	return
+}