bitwarden/src/Core/Utilities/StrictEmailAddressAttribute.cs

using System.ComponentModel.DataAnnotations;
using System.Text.RegularExpressions;
using MimeKit;

namespace Bit.Core.Utilities
{
    public class StrictEmailAddressAttribute : ValidationAttribute
    {
        public StrictEmailAddressAttribute()
            : base("The {0} field is not a supported e-mail address format.")
        {}
        
        public override bool IsValid(object value)
        {
            var emailAddress = value?.ToString();
            if (emailAddress == null)
            {
                return false;
            }

            try
            {
                var parsedEmailAddress = MailboxAddress.Parse(emailAddress).Address;
                if (parsedEmailAddress != emailAddress)
                {
                    return false;
                }
            }
            catch (ParseException)
            {
                return false;
            }

            /**
            The regex below is intended to catch edge cases that are not handled by the general parsing check above.
            This enforces the following rules:
            * Requires ASCII only in the local-part (code points 0-127)
            * Requires an @ symbol
            * Allows any char in second-level domain name, including unicode and symbols
            * Requires at least one period (.) separating SLD from TLD
            * Must end in a letter (including unicode)
            See the unit tests for examples of what is allowed.
            **/
            var emailFormat = @"[\x00-\x7F]+@.+\.\p{L}+$";
            if (!Regex.IsMatch(emailAddress, emailFormat))
            {
                return false;
            }

            return new EmailAddressAttribute().IsValid(emailAddress);
        }
    }
}