Here are the steps to convert a user to a shared mailbox in Microsoft 365 admin:
- Log in to the Microsoft 365 admin center with your administrator account.
- Go to the Users section and select Active Users.
- Find the user you want to convert to a shared mailbox and select their name.
- Select Mail tab
- Select convert to shared mailbox.
- Follow the prompts to complete the conversion process.
- Assign the required permissions to the users who will have access to the shared mailbox.
- Update email client settings for the users who will access the shared mailbox
Note: Once the user is converted to shared mailbox, the user will lose access to other services (besides Exchange email) and will not be able to login to the account.