That's a really good question. This FAQ on duplicate contacts should help to answer your question- it explains the ways in which our system identifies those contacts. Also, if there's anyone that's signed up for your list with various different email addresses then this FAQ can help show you how to merge them into one contact. I hope those help, but if you have any other questions please let us know!
You can post a new message in the Community or find us on Twitter Mon-Fri 8am-8pm ET, Sat 10am-8pm ET, & Sun 10am-6pm ET. We've got real people waiting to help you out. Click below to start a conversation!