If you want someone else to be seen as the sender, they need to be the listed owner of the envelope. This can be accomplised two ways.

1) Either they are the original sender of the envelope. Simply create a user account for the Group Mailbox that you want to send from and then login to DocuSign from there when sending.

2) (https://support.docusign.com/en/guides/ndse-admin-guide-custody-transfer) Transfer the Cutosdy of the envelope once it has been created. Be warned though that unless you put in an automatic transfer rule or a stopgap before the first recipient, the recipient will see the original owner of the envelope before receieving a notice from the new owner.

Hope this helps.

As suggests, creating an Envelope Transfer Rule and then checking 'Prior to first send' will cause all envelopes to appear to be delivered from the generic user instead. Note that this does fully change ownership of the document, so you may way to set up Document Sharing so that senders will still have access to Correct or Void envelopes.