C# Online Compiler | .NET Fiddle

using System;using System.Text; using System.Linq;
//https://metadataconsulting.blogspot.com/2021/01/CSharp-dotNet-How-to-get-all-emails-from-a-HTML-page-with-a-href-inner-text.html					
public class Program
{
	
	/// <summary>
	/// Extract a href with mailto (emails) links with inner text
	/// </summary>
	public static string ExtractEmailswithInnerText(string s)
	{
		string mailto = "mailto:"; 
		//removal ASCII and UNICODE control characters
		string h = new String(s.Where(c => !char.IsControl(c)).ToArray());

		StringBuilder sb = new StringBuilder(h.Length); 
		
		try
		{
			HtmlAgilityPack.HtmlDocument htmldoc  = new HtmlAgilityPack.HtmlDocument();
			htmldoc.LoadHtml(h);
			//var urls = html.DocumentNode.SelectNodes("//a[@href!='']").Select(i => i.Attributes["href"].Value);

			if (htmldoc.DocumentNode.SelectNodes("//a/@href").Count > 0)
			{

				foreach (HtmlAgilityPack.HtmlNode node in htmldoc.DocumentNode.SelectNodes("//a/@href"))
				{
					if (node.Name == "a")
					{
						//probably a good idea to HttpUtility.HtmlDecode(node.InnerText).Trim() 
						if (node.Attributes["href"].Value.StartsWith(mailto))
							sb.AppendLine(string.Concat(node.InnerText.Trim(), " <", node.Attributes["href"].Value.Replace(mailto, string.Empty), ">"));
					}

				}

				return sb.ToString();
			}
			else
			{
				return string.Empty;
			}
		}
		catch //(Exception ex)
		{
			//bad formed HTML error handle it
		}

		return string.Empty;
	}
	
	public static void Main()
	{
		string html = "<a href=\"https://trojanhorsethebook.com/wordpress/\">Home</a><div class=\"footerLeft\"><p>©<script type=\"text/javascript\">copyright=new Date();update=copyright.getFullYear();document.write(update);</script>2021      Mark Russinovich.  All Rights Reserved.</p>    <p>Email: <a href=\"mailto:mark@russinovich.com\">mark@russinovich.com</a></p></div>";
		//Best practice, we should check for this empty case, but not really common, defeats purpose
		//string html2 = "<a href=\"https://trojanhorsethebook.com/wordpress/\">Home</a><div class=\"footerLeft\"><p>©<script type=\"text/javascript\">copyright=new Date();update=copyright.getFullYear();document.write(update);</script>2021      Mark Russinovich.  All Rights Reserved.</p>    <p>Email: <a href=\"mailto:mark@russinovich.com\"></a></p></div>";
		string html3 = "<div id=\"post\"><article class=\"article single\"><header class=\"article-header\"><h1>Contact</h1></header><div class=\"article-content\"><p>If you have any questions, comments or concerns, please email help@thurrott.com</p></div></article> </div>"; 
		Console.WriteLine(ExtractEmailswithInnerText(html));
		Console.WriteLine(ExtractEmailswithInnerText(html3));
	}
}

 
using System;using System.Text; using System.Linq;
//https://metadataconsulting.blogspot.com/2021/01/CSharp-dotNet-How-to-get-all-emails-from-a-HTML-page-with-a-href-inner-text.html                  
public class Program
{
    
    /// <summary>
    /// Extract a href with mailto (emails) links with inner text
    /// </summary>
    public static string ExtractEmailswithInnerText(string s)
    {
        string mailto = "mailto:"; 
        //removal ASCII and UNICODE control characters
        string h = new String(s.Where(c => !char.IsControl(c)).ToArray());
​
        StringBuilder sb = new StringBuilder(h.Length); 
        
        try
        {
            HtmlAgilityPack.HtmlDocument htmldoc  = new HtmlAgilityPack.HtmlDocument();
            htmldoc.LoadHtml(h);
            //var urls = html.DocumentNode.SelectNodes("//a[@href!='']").Select(i => i.Attributes["href"].Value);
​
            if (htmldoc.DocumentNode.SelectNodes("//a/@href").Count > 0)
            {