Best way to mass change email addresses?

Hi everyone,

My company just changed our domain name, and we use marketo for all employee notifications. I'd like to change the email addresses on the lead records for our employees to the new one, and I was wondering if there was a better way to do that than manually going through every record. Normally to make a change like this, I would export all of the fields that need changing along with their email address and then reimport the list after making the changes, so that marketo matched the email addresses and updated the fields in the spreadsheet, but since these are different email addresses, I don't know how to get Marketo to not create new leads instead of just updating the old ones.

Any ideas?

Thanks!