Hi RHouser,
I would like to confirm some information:
-What do you mean by saying “many email accounts used by one user”?
-Which plan of Office 365 have you subscribed? Small Business, Midsize Business or Enterprise?
You can add proxy addresses to the primary mailbox so that any email sent to the proxy address is delivered to the primary mailbox. Notice: You cannot send e-mails from the proxy address.
To add the proxy address, follow the steps below:
1. Login to Office 365 Portal (https://portal.micosoftonline.com/) with administrator account.
2. Go to Exchange Admin Center.
a. For Office 365 Small Business:
1) Click Outlook to access Outlook Web App.
2) Change the URL address from https://podxxx.outlook.com/owa/... to https://podxxx.outlook.com/ecp to enter the Exchange admin center.
b. For Office 365 Enterprise or Midsize: click Admin>Exchange.
3. Click recipients>mailboxes then select a mailbox and click the edit icon.
4. Select email address and click the add icon. The screenshot below is for your reference:
Best Regards,
Bruce Zhou