It is possible to update the email address of an Office 365 account. Here are the steps you can follow:

1. Go to the Office 365 admin center and sign in with your admin account.
2. Click on the “Users” tab in the left-hand menu.
3. Select the user whose email address you want to update.
4. Click on the “Edit” button next to the user’s email address.
5. Enter the new email address in the “Email” field.
6. Click on “Save” to update the email address.

Please note that changing the email address will also change the user’s login name, so you may need to update any external systems or applications that use the old email address as a username. Additionally, changing the email address may affect any email rules or settings that the user has configured, so you should advise the user to review their email settings after the update.

You can create a mail flow rule to block the sender’s email address in the new Exchange admin center. Here are the steps:

1. Sign in to the new Exchange admin center at https://admin.exchange.microsoft.com/
2. Go to Mail flow > Rules
3. Click + to create a new rule
4. In the New rule page that opens, enter a name for the rule
5. Under Apply this rule if, select The sender…
6. Select is this person and enter the email address of the sender you want to block
7. Under Do the following, select Block the message
8. Click Save to save the new rule