Once the linked mailbox is created, you can manage permissions and access to it. Here are the steps to do so:

• In the Exchange Admin Center, click on "Recipient" and then "Mailboxes".

• Search for the linked mailbox you want to manage and select it.

• Click on "Manage mailbox permissions" to add or remove permissions for the mailbox.

• Click on "Manage full access permission" to assign users or groups full access to the mailbox.

• Click on "Manage send as permission" to assign users or groups the ability to send messages as the mailbox.
  

Remove a Linked Mailbox

• In the Exchange Admin Center, click on "Recipient" and then "Mailboxes."

• Search for the linked mailbox you want to remove and select it.

• Click on the "..." icon and then click on "Delete."

• Follow the prompts to confirm the deletion.

Note that removing a linked mailbox will also remove the corresponding Office 365 mailbox. Therefore, make sure to inform users of the mailbox's removal and advise them to save any important data before the deletion.

To configure a linked mailbox in Exchange Online, follow these steps:

1. Prepare the on-premises environment: Before you can create a linked mailbox in Exchange Online, you need to prepare the on-premises environment. This includes setting up a remote domain in Exchange Online and creating a user account with the necessary permissions in the on-premises Active Directory. You also need to configure the necessary network connectivity between your on-premises environment and Exchange Online.

2. Create the linked mailbox: After you've prepared the on-premises environment, you can create the linked mailbox in Exchange Online. To do this, follow these steps:

3. a. Sign in to the Microsoft 365 admin center with your admin credentials.

4. b. Click on "Exchange" in the left-hand menu.

5. c. Click on "Recipients" and then select "Migration."

6. d. Click on the "+" icon and then select "Migrate to Exchange Online."

7. e. Select "Remote move migration" and then click "Next."

8. f. Enter the user account information for the on-premises mailbox that you want to link, and then click "Next."

9. g. Select the Exchange Online mailbox that you want to link the on-premises mailbox to, and then click "Next."

10. h. Configure the migration settings as needed, such as the migration endpoint and batch name, and then click "New."

11. i. Wait for the migration batch to complete. This can take some time, depending on the size of the mailbox and the network bandwidth available.

12. Configure permissions: After the linked mailbox is created, you need to configure the necessary permissions for the on-premises user account to access the linked mailbox in Exchange Online. This includes granting the user account the necessary Exchange Online permissions and configuring the mailbox permissions in the on-premises Active Directory.

By following these steps, you can create a linked mailbox in Exchange Online and link it with a mailbox in your on-premises environment. This allows you to move mailboxes between the two environments as needed, and ensures that users have access to their mailbox regardless of where it's located.