Existing users get e-mail after import new users

I manage a site of an association with about 250 members. To update the member file I recently started using the plugin “Import and export users and customers”. The very first import went well. Everyone received an email with login details. Now I have made an update, but now existing members receive an email from WP (?) with the content:

This message confirms that your email address has been changed at xyz.nl.
If you have not changed the email address, please contact the site administrator at [email protected]

I have disabled send emails in the plugin and it still happens. I messed around with it which caused the members to receive this email 3 times …

Please advise!