using System;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		string pattern = @"(?:To:\s+|\G(?!^))(?:,\s*)?([^\s@,]+@[^\s@,]+)";
        string input = @"To: sandy.lewis@test.com,alewis@testpage.com, drtmirk@test.org.au ,";
        RegexOptions options = RegexOptions.Multiline;
 
        foreach (Match m in Regex.Matches(input, pattern, options))
        {
            Console.WriteLine(m.Groups[1].Value);
        }
	}
}

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