Whitelisting email addresses
If you're looking to only allow certain email addresses to place an order, you may want to use our beta RSVPs feature. This allows you to create a unique "invitation" URL that can only be used once, and send it out to specific people via email. Contact us to request access.
Blacklisting email addresses
So far, we have opted not to implement this in Tito. It is very easy for people to get around such a feature (for instance by exploiting Gmail's plus and period workarounds), or use a temporary/disposable email address. If you'd like to prevent people from registering with their personal email addresses (e.g. gmail.com, yahoo.com, etc.), you could either consider using our beta RSVPs feature if you have a specific list of people to invite, or else enable the waiting list on a ticket and manually reject or offer a ticket on a case by case basis.
Restricting email addresses to one order each
You can set an order limit of "1" on tickets so that people will only be able to buy a single ticket at a time, however this would not prevent someone from placing a separate registration with the same email address. We've built it this way to allow for people to place orders on behalf of other people, and assign them their tickets. Read more about Tito's checkout flow.