A. Create a secondary domain, mystartup.com, within your current Google Workspace domain, set up necessary DNS records, and create all startup employees with the secondary domain as their primary email addresses.

B. Create an alias domain, mystartup.com, in your existing Google Workspace domain, set up necessary DNS records, and create all startup employees with the alias domain as their primary email addresses.

C. Create a new Google Workspace domain with "mystartup.com," and create a trust between both domains for reusing the same security policies and sharing employee information within the companies.

D. Create the startup employees in the "mycompany.com' domain, and add a number at the end of the user name whenever there is a conflict. In Gmail > Routing, define a specific route for the OU that targets the startup employees, which will modify the email address domain to "mystartup.com," and remove any numbers previously added. In addition, confirm that the SPF and DKIM records are properly set.