This is from Notification E-mail Header:
From: Contoso IT HelpDesk helpdesk.noreply@domain.com
To: user@domain.com
Return-Path: helpdesk@domain.com
My Outlook (same domain and Exchange tenant as Zammad mainbox) shows this mail as from helpdesk@domain.com and I am unable to change this.
Third party mailbox show the same, all mail goes from helpdesk@domain.com