How to Remove an alias from a shared mailbox

Step 1: Sign in to the Office 365 portal.

Step 2: Go to Groups > Shared mailboxes, and then select the shared mailbox from the list.

Step 3: In the Name, Email, and Email aliases section, select Edit.

Step 4: In the Email aliases section, remove the email address by selecting the remove (wastebin) icon, and then Save.