Improve flexibility of email validation in the ValidationHelper

* ValidationHelper.EmailRegEx can now be modified to suit the users needs
* Regex updated to be more inclusive - see https://html.spec.whatwg.org/#valid-e-mail-address

framework/src/Volo.Abp.Validation/Volo/Abp/Validation/ValidationHelper.cs

@@ -4,7 +4,9 @@ namespace Volo.Abp.Validation
 {
     public class ValidationHelper
     {
-        private const string EmailRegEx = @"[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?";
+        // Taken from W3C as an alternative to the RFC5322 specification: https://html.spec.whatwg.org/#valid-e-mail-address
+        // The RFC5322 regex can be found here: https://emailregex.com/
+        public static string EmailRegEx { get; set; } = @"^[a-zA-Z0-9.!#$%&'*+\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$";
 
         public static bool IsValidEmailAddress(string email)
         {
@@ -13,7 +15,6 @@ namespace Volo.Abp.Validation
                 return false;
             }
 
-            /*RFC 2822 (simplified)*/
             return Regex.IsMatch(email, EmailRegEx, RegexOptions.Compiled | RegexOptions.IgnoreCase);
         }
     }