GSM is offered as "free" and "registered" version. Mails sent with the free version will have a line in the bottom with "powered by GSM" or another text from a sponsor. If you are using GSM in commercial or professional purpose you may want to remove this link - that´s the registered version. As registered user you also will have a priority service and full access to upcoming features.
You can register a single email addresses - or - your entire domain (wich is used in gmail) for all of your email addresses with this domain. A domain registration covers all of your email addresses without limitation.
If you have questions to the registration, please contact me directly: MAIL