Hi Peter,
As I understand it, you need to get all the emails from the four email accounts into one mailbox. If there is any misunderstanding, please correct me.
Based on my experience, to achieve this, you can add another three email accounts as the mailbox’s proxy address. But the proxy address does not actually existed mailbox, and the proxy address cannot send mails.
Detail information please refers to the following link: help.outlook.com/.../cc511403.aspx
Thanks,
Anna Shi