Modify Groups Email Address

Hi,

I am using OWA to create groups.

My problem is that when I create a new group, by default an email address with below extension will be assign to it:

NewGroup@Mycompany.onmicrosoft.com

I want to add NewGroup@Mycompany.com.au  as an alias to this email but I have no option for modification.

Please help.

Thank you

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