When teammates leave to pursue new opportunities, sometimes we want to retain their email, without paying for the cost of another mailbox.
Best practices in such cases are to open a support ticket with the subject: "Copy email for username@mydomain.com to username2@mydomain.com" where username is the mailbox of the teammate who's left your team, and username2 is the mailbox of the teammate who's staying, and wants access to username's email.
In the body of the support ticket, confirm what's happening, and when you want to it happen.
Once we receive the request, we'll work on moving the mail from the old teammate's mailbox into a new folder/directory of your existing teammate's mailbox.
Once we have done that, we'll delete the old employee's mailbox (let us know if you don't want this to happen), and create an email alias of username for the existing teammate's mailbox (username2), so any mail coming in for them will still be received, and may be responded to by username2.
What's more, username2 may share the username email folder/directory to other teammates who may also want access to username's old email.
Finally, username2 can use filters to automatically drop any new mail that comes in for username directly into their folder, and if you've shared that folder to others, they'll also see the new mail as it comes in.
Hope this is useful and makes sense! Welcome feedback and questions.