EPiServer Mail can be registered using CMS, Create+ and Relate+ Developer Licenses.
Everyone can activate their license through the same procedure, the very one you are referring to. Please note that if you are using a developer license for a specific end project, please fill in the form accordingly if the same broker account configuration will be used at deployment.
The information you supply will be associated with any additional licenses that will be installed on the configured environment. As soon as a commercial license is found, all developer restrictions will be removed. To view what restrictions apply to your planned mailing, after setting "now" or scheduled time for sending, click "View restriction" in the last step of your mailing creation.
Currently, the developer restrictions are 10 recipients per ordermail, max 60 ordermails a minute and a total of 1000 recipients.
You can find the related information of the EPiServer Mail restrictions here:
But as far as I can see, there is no information regarding the restriction displayed on the EPiServer Mail panel inside EPiServer. So if you of some reason have forgotten to click the link you got on the mail on the first activation email you got, you are still in developer modus until the click has been done. No reminders are sent.
Clicking on the link will remove the restrictions in EPiServer Mail immediately.