Could you please explain what would be the impact if a person's email id is configured in Sender/Reply back address of a delivery? Can you also highlight the significance of having a separate mail box as the Sender and Reply back address if keeping a persons's email account as Sender address is not a best practice?
Sender is who the message is from (mandatory 'From' header), Reply is where reply emails should be sent (optional 'Reply-to' header).
They can be different with no impact to deliverability. From address has strict security restrictions on the subdomain it can use, reply-to has none. Best practice is to have a person that can be contacted as either address, and not use no-reply or autoresponders. More info in rfc5322-3.6.2: http://www.rfc-editor.org/rfc/rfc5322.txt