ZeroBounce.net automatically removes duplicate records and mal-formed email addresses from all files you upload to be processed.
For example, if you upload 1000 emails and 10 of those emails are duplicates, once processing finishes, you will see 990 emails processed. We didn't lose any emails you uploaded, we just eliminated the duplicates.
You are not charged any credits for duplicate or mal-formed emails. We simply ignore them.