need assistance with a powershell script for adding additional email alias

hello, can someone help me modify the following script to work on a non-exchange server. [we are in dirsync mode with office 365 and have removed Exchange on-premise.
I need to modify this to key on the proxyAddresses attribute rather than emailAddresses so I can run this on a domain controller [not an exchange server]

Import-Csv alias-add-pipe.csv | % {
$user = Get-user $_.SMTP 
$user.emailAddresses += $_.newsmtp
Set-Mailbox $user -emailAddresses $user.emailAddresses
}

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