Mailto email obfuscation helper

MailToHelper.cs

using System.Text.RegularExpressions;

namespace Gosso.Mvc.Helpers
{
    public class MailToHelper
    {
       
        private static readonly string replaceTemplate = @"#"" onclick=""window.location = 'mailto:' + ['{0}'].join(''); return false;";

        public static string TransformMailToLinks(string text)
        {
            Regex regex = new Regex(@"mailto:([^""]+)");
            var matches = regex.Matches(text);

            if (matches.Count > 0)
            {
                foreach (Match match in matches)
                {
                    var email = match.Groups[1]?.Value;

                    var emailAfter = string.Join("','", email.ToCharArray());
                    Regex regReplace = new Regex(match.Value.Replace("?",@"\?"));
                    text = regReplace.Replace(text, string.Format(replaceTemplate, emailAfter), 1);//only replace first occurancy
                }
            }

            //now replace any email in plain text
            regex = new Regex(@"([a-zA-Z0-9._-]+@[a-zA-Z0-9._-]+\.[a-zA-Z0-9_-]+)");
            matches = regex.Matches(text);
            if (matches.Count > 0)
            {
                foreach (Match match in matches)
                {
                    var email = match.Groups[1]?.Value;
                    text = text.Replace(email, email.Replace("@", @" [at] "));
                }
            }
            return text;
        }
    }
}

MailtoReplaceTests.cs

using Gosso.Mvc.Helpers;
using Xunit;
namespace XUnitTest
{
    public class MailtoReplaceTests
    {     
        [Fact]
        public void MailtoTest()
        {
            var testStr = @"<p><a href=""mailto:[email protected]""> test
                whateva <a href=""mailto:[email protected]?subject=title of subject""> whateva <a href=""https://www.secondo.uk.com/"">test</a>
                whateva <a href=""mailto:[email protected]""> sdf</p>";
            var output = MailToHelper.TransformMailToLinks(testStr);
            Assert.Contains("['l','o','u','i','s','@','t','r','e','s','.','s','e']", output);
        }

        [Fact]
        public void MailtoTest2()
        {
            var testStr = @"test <a href=""mailto:[email protected]""> whateva
                whateva <a href=""mailto:[email protected]?test=yes""> whateva
                whateva <a href=""mailto:[email protected]""> whateva";
            var output = MailToHelper.TransformMailToLinks(testStr);
            Assert.StartsWith(@"test <a href=""#"" onclick=""window.location = 'mailto:' + ['l','u','c','@','f','i','r','s','t','.','s','e'].join(''); return false;"">", output);
        }

        [Fact]
        public void MailtoTest3()
        {
            var testStr = @"test <a href=""mailto:[email protected]"">[email protected]</a> test
                whateva <a href=""mailto:[email protected]?test=yes""> whateva
                whateva <a href=""mailto:[email protected]""> whateva";
            var output = MailToHelper.TransformMailToLinks(testStr);
            Assert.StartsWith(@"test <a href=""#"" onclick=""window.location = 'mailto:' + ['l','u','c','@','f','i','r','s','t','.','s','e'].join(''); return false;"">", output);
            Assert.Contains(@"luc [at] first.se</a> test", output);
        }

        [Fact]
        public void Mailto_second_and_third_formatchange()
        {
            var testStr = @"<p><a href=""mailto:[email protected]""> whateva
                whateva sdfdfs secondo <a href=""mailto:[email protected]?test=yes""> test <a href=""https://www.secondo.uk.com/"">test</a>
                tres <a href=""mailto:[email protected]""> whateva</p>";
            var output = MailToHelper.TransformMailToLinks(testStr);
            Assert.Contains(@"secondo <a href=""#"" onclick=""window.location = 'mailto:'", output);
            Assert.Contains(@"tres <a href=""#"" onclick=""window.location = 'mailto:'", output);
        }

        [Fact]
        public void Mailto_second_and_third_sameAddress()
        {
            var testStr = @"<p><a href=""mailto:[email protected]""> whateva </a>
            whateva whateva secondo <a href=""mailto:[email protected]?test=yes""/> test <a href=""https://www.secondo.uk.com/"">test</a>
            tres <a href=""mailto:[email protected]""/> sdf</a></p>";
            var output = MailToHelper.TransformMailToLinks(testStr);
            Assert.Contains(@"<a href=""#"" onclick=""window.location = 'mailto:' + ['l','u','c','@','f','i','r','s','t','.','s','e'].join", output);
            Assert.Contains(@"'l','u','c','@','f','i','r','s','t','.','s','e','?','t','e','s','t','=','y','e','s'].join('')", output);
        }

    }
}