When you import a .CSV file of contacts - whether you're adding guests to an event or recipients to an email - Splash automatically removes duplicate email addresses. This ensures you aren't spamming the same guests over and over - and that you keep clean, up to date contacts.
If you need to add multiple guests with the same email address, you can add them one by one. If the email address is a placeholder, you can use unique format for each contact, like firstname.lastname@example.org. Just be sure to not use your own email address!
When guests RSVP to my event will duplicate email addresses be removed?
Nope, your guests can RSVP multiple times to your event unless you turn on the "Limit one response per email" setting in the Form tab of your event.
For more insight, check out our FAQ: 5/4/17 - Monitor the status of guest list imports & exports