yes it is possible to write your own messages into the log file.
var client = new Telnet(server, port);
client.LogWriter = new Rebex.FileLogWriter("MyLog.log", Rebex.LogLevel.Verbose);
// you can write custom messages to the log using the LogWriter.Write method like this:
client.LogWriter.Write(Rebex.LogLevel.Debug, typeof(Imap), instanceID, "MyArea", "MyMessage");
If you have just one instance of Telnet, just use instanceID = 0. If you are using multiple instances, you can use different instanceID's to differentiate it in the log file.