void Main() {
	var logItems = GetLogItems();

	var Messages = logItems.Select(item => new {
			From = extractFromEmailFromMessage(item.Message),
			SentToList = extractToEmailsFromMessage(item.Message)
		}).ToList();

	var MessagesGroupByFrom = Messages
		.OrderBy(x => x.From)
		.GroupBy(x => x.From)
		.Select(x => new {
			From = x.Key,
			SentTo = x.SelectMany(y => y.SentToList)
				.GroupBy(y => y)
				.Select(g => new {
					To = g.Key,
					Count = g.Count()
				}).ToList()
		}).ToList();

	MessagesGroupByFrom.ForEach(fromEmail => {
		Console.WriteLine($"--- {fromEmail.From} ---");
		fromEmail.SentTo.ForEach(toObj => {
			Console.WriteLine($"     {toObj.To}  Count: {toObj.Count} ");
		});
	});

}

class LogItem
{
	public string Message;
	public string SessiongId;
	public string From;
	public string To;
}

List<string> extractToEmailsFromMessage(string text) {
	var toPattern = @"to:\s+(\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*)";
	var toRegex = new Regex(toPattern, RegexOptions.IgnoreCase);

	var matches = new List<string>();
	foreach (Match match in toRegex.Matches(text)) {
		matches.Add(match.Groups[1].Value?.ToLower());
	}

	return matches;
}

string extractFromEmailFromMessage(string text) {
	var fromPattern = @"from:\s+(\w+([-+.']\w+)*@)\w+([-.]\w+)*\.\w+([-.]\w+)*";
	var fromRegex = new Regex(fromPattern, RegexOptions.IgnoreCase);

	var match = fromRegex.Match(text);
	if (match.Success) {
		return match.Groups[1].Value.ToLower();
	}
	return "";
}

List<LogItem> GetLogItems() {
	return
		new List<LogItem> {
		new LogItem() {  Message = "from: rik@zoom.com to: paul@blah.com to: sally@blah.com", SessiongId = "123" },
		new LogItem() {  Message = "from: rik@zoom.com to: alex@blah.com to: paul@blah.com", SessiongId = "123" },
		new LogItem() { Message = "from: joe@blah.com to: alex@blah.com ", SessiongId = "123" },
		new LogItem() { Message = "from: paul@blah.com to: Nancy@blah.com", SessiongId = "124" },
		new LogItem() { Message = "from: alex@blah.com to: paul@blah.com to: nancy@blah.com to: sally@blah.com", SessiongId = "124" },
		new LogItem() { Message = "from: nancy@blah.com to: joe@blah.com to:  tim@whoville.com", SessiongId = "125" },
		new LogItem() { Message = "from: joe@blah.com to: alex@blah.com to: paul@blah.com", SessiongId = "125" },
		new LogItem() { Message = "from: alex@blah.com to: Paul@blah.com to:  sally@blah.com to: nancy@blah.com", SessiongId = "126" },
		new LogItem() { Message = "from: Paul@blah.com to: joe@blah.com to:  jim@blah.com", SessiongId = "126" },
		new LogItem() { Message = "from: alex@blah.com to: view@blah.com to:  paul@blah.com", SessiongId = "126" },
	};
}