Diobox has a special email invitation feature that incorporates a built-in RSVP Form for the invitation process.

This type of email allows you to collect RSVPs for a private (by-invite-only) event. The process generates a unique RSVP link for each recipient when the emails are sent. Then, when the recipient clicks through from the email, they are asked to accept or decline the invitation, making the RSVP non-transferrable. As a result, only the recipient can register for the event and it prevents them from sharing the link with anyone else.

Go to the Emails tab and click + Email button on the upper-right side of the screen.

Select any of the templates under the Email with Built-In RSVP Tracking section.

After setting up the email and customizing the message, you can manage RSVP settings (on the 4th page of the Email Builder):

When the emails are sent, each message will include a unique link for each recipient. As a result, only the recipient can register for the event and it prevents them from sharing the link with anyone else.