If you lose the e-mail with a ticket, you can use your user name (your email) and password you received when you purchased tickets.
It is necessary to open the page for user logging where you enter the user name (your email) and password you received when you purchased tickets. After that, click on the link Your Tickets & Accounts and at the top center of the screen you will find the ticket and the invoice that you bought through Croatia Tickets service.
Another way to recovery tickets and invoices to your e-mail is to contact customer support.