Shared Mailbox multiple domains

[Tyler Martin]

I've got 3 unique domains that each currently have their own admin@ account. I want to manage all three domains on one tenant, but I cant seem to have multiple shared mailboxes with the same prefix ie:

admin@domain1.com

admin@domain2.com

admin@domain3.com

The user who monitors these mailboxes needs to be able to send uniquely from all of those domains. Is this possible?

[#2]

You can, simply don't use the Admin center to create them - it tries to enforce uniqueness of the "alias" and forgets to check the different domain name. Use PowerShell to create them, or simply create them with different alias and change it later.

[#3]

What would the commands be to set them up in Powershell? 

I tried to set them up uniquely in Exchange Admin, and then change them after but it failed, it still wasn't looking at the domain. 

[#4]

It's simple:

New-Mailbox -Name Shared1 -Shared -PrimarySmtpAddress shared@domain1.com

If needed, also use the -Alias parameter.

[#5]

Got this issue with this but powershell ain't my forte at that time so i followed a UI version with below article.
https://www.thedailyexploits.co/using-same-alias-for-shared-mailbox-in-multiple-domain/