Outlook multiple email domains

I would like to see MULTIPLE domains in my Mailbox

email address removed for privacy reasons

email address removed for privacy reasons

email address removed for privacy reasons

I'm sure this was possible on Exchange 2016

I found this:

https://docs.microsoft.com/en-us/exchange/recipients/user-mailboxes/email-addresses?view=exchserver-2019

Alias is no good as the email arrives in the mailbox fine but TO address dosen't show up!

Adding smtp is the same

Help suggests use email type as PROXY rather than SMTP but which email seems to be accepted - it dosen't arrive in my mailbox... nor is it rejected

I can't believe O365/Outlook does not support this !

BTW: INCOMING not Outgoing