A – Dynamic DNS is a web service requiring registration. It use a straight forward client to send updates to the database of addresses.
You don’t specify which DSL, or if the Sonic Firewall is providing NAT internally. If NAT’ed the simple scripts won’t work as they read from IPCONFIG.
Try a macro recorder to follow the steps as you get the DSL’s IP address at the console. If that works you have your script and only need the e-mail function.
The simplest answer is Dynamic DNS.