Create new AD Object , then Enable it for Remote Mailbox

Enable-RemoteMailbox -Shared "Kim Akers" -RemoteRoutingAddress "[email protected]"

After this make sure you change the SMTP Address as it will create it with the default SMTP address from address book policy

Create new remote mailbox from scratch

New-RemoteMailbox -Shared -Name "Mailboxname" -Firstname "FirstName" -LastName "LastName" -UserPrincipalName "email -OnPremisesOrganizationalUnit"OU=Shared Mailboxes,OU=xxxxx,OU=xx Users,DC=xxx,DC=local" -RemoteRoutingAddress [email protected]

After this make sure you change the SMTP Address as it will create it with the default SMTP address from address book policy