From 0dc0ce3a26371ccf7c31b2c68c4218962cf28647 Mon Sep 17 00:00:00 2001
From: Miles Faciane <39567252+milesfaciane@users.noreply.github.com>
Date: Fri, 31 May 2024 12:09:09 -0500
Subject: [PATCH 1/2] Return error when no MX records

If LookupMX returns no records, return an Error instead of causing a panic.
---
 checkmail.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/checkmail.go b/checkmail.go
index 712c6bd..6990187 100644
--- a/checkmail.go
+++ b/checkmail.go
@@ -33,6 +33,7 @@ const forceDisconnectAfter = time.Second * 5
 var (
 	ErrBadFormat        = errors.New("invalid format")
 	ErrUnresolvableHost = errors.New("unresolvable host")
+	ErrNoMXRecord       = errors.New("host DNS does not have MX records")
 
 	emailRegexp = regexp.MustCompile(`(?m)^(((((((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)|(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?"((\s? +)?(([!#-[\]-~])|(\\([ -~]|\s))))*(\s? +)?"))?)?(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?<(((((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?(([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+(\.([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+)*)((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)|(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?"((\s? +)?(([!#-[\]-~])|(\\([ -~]|\s))))*(\s? +)?"))@((((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?(([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+(\.([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+)*)((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)|(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?\[((\s? +)?([!-Z^-~]))*(\s? +)?\]((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)))>((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?))|(((((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?(([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+(\.([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+)*)((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)|(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?"((\s? +)?(([!#-[\]-~])|(\\([ -~]|\s))))*(\s? +)?"))@((((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?(([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+(\.([A-Za-z0-9!#-'*+\/=?^_\x60{|}~-])+)*)((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?)|(((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?\[((\s? +)?([!-Z^-~]))*(\s? +)?\]((((\s? +)?(\(((\s? +)?(([!-'*-[\]-~]*)|(\\([ -~]|\s))))*(\s? +)?\)))(\s? +)?)|(\s? +))?))))$`)
 )
@@ -79,6 +80,9 @@ func ValidateHostAndUser(serverHostName, serverMailAddress, email string) error
 	if err != nil {
 		return ErrUnresolvableHost
 	}
+	if len(mx) == 0 {
+		return ErrNoMXRecord
+	}
 	client, err := DialTimeout(fmt.Sprintf("%s:%d", mx[0].Host, 25), forceDisconnectAfter)
 	if err != nil {
 		return NewSmtpError(err)

From ddd9be170557a8b0333d8121d234311fd3ca307d Mon Sep 17 00:00:00 2001
From: Miles Faciane <39567252+milesfaciane@users.noreply.github.com>
Date: Mon, 3 Jun 2024 11:31:37 -0500
Subject: [PATCH 2/2] Update checkmail.go

If there are no mx records, return ErrNoMXRecord.
---
 checkmail.go | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/checkmail.go b/checkmail.go
index 6990187..84ad6b5 100644
--- a/checkmail.go
+++ b/checkmail.go
@@ -48,8 +48,10 @@ func ValidateFormat(email string) error {
 // ValidateMX validate if MX record exists for a domain.
 func ValidateMX(email string) error {
 	_, host := split(email)
-	if _, err := net.LookupMX(host); err != nil {
+	if mx, err := net.LookupMX(host); err != nil {
 		return ErrUnresolvableHost
+	} else if len(mx) == 0 {
+		return ErrNoMXRecord
 	}
 
 	return nil
@@ -61,6 +63,8 @@ func ValidateHost(email string) error {
 	mx, err := net.LookupMX(host)
 	if err != nil {
 		return ErrUnresolvableHost
+	} else if len(mx) == 0 {
+		return ErrNoMXRecord
 	}
 	client, err := DialTimeout(fmt.Sprintf("%s:%d", mx[0].Host, 25), forceDisconnectAfter)
 	if err != nil {
@@ -79,8 +83,7 @@ func ValidateHostAndUser(serverHostName, serverMailAddress, email string) error
 	mx, err := net.LookupMX(host)
 	if err != nil {
 		return ErrUnresolvableHost
-	}
-	if len(mx) == 0 {
+	} else if len(mx) == 0 {
 		return ErrNoMXRecord
 	}
 	client, err := DialTimeout(fmt.Sprintf("%s:%d", mx[0].Host, 25), forceDisconnectAfter)