Is there a way to prevent duplicate customers in zoho subs using the email address as the unqiue key

Is there a way to prevent duplicate customers in zoho subs using the email address as the unqiue key

We often get duplicate customer records in Zoho Subscriptions - two records having the same email address which causes a lot of havoc.   Is there a way to require the email address to be unqiue in zoho subs?