@irfan
You cannot disable the completion email in DocuSign eSignature. It will be sent to all recipients in the workflow, unless it is an embedded recipient for which you can disable the email notifications.
A user is able to configure in his account which email notifications from DocuSign he wants to receive and could opt-out from other email notifications.
DocuSign Support Article on Email Notifications:
https://support.docusign.com/s/articles/How-do-I-manage-my-email-notifications?language=en_US
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