Replace Primary SMTP Address | AD

I've recently had to replace the Primary SMTP address for all users within an organisation.  Of course this is a lot easier if you script it.

I needed to do this as the client was changing their primary address, but wanted to retain all the current proxyAddresses as well.

This was achieved by using two scripts.

$Users = Get-ADUser -SearchBase 'OU=ouname,OU=ouname,OU=ouname,OU=ouname,DC=domai,DC=com,DC=au' -Filter * -Properties mail,ProxyAddresses | Select-Object samaccountname,ProxyAddresses
    
Foreach ($User in $Users)

            {
            $Samaccountname = $User.samaccountname
            $SMTP = "SMTP:$samaccountname@newdomain.com.au"
            Set-ADUser $samaccountname -Add @{proxyAddresses=$SMTP}
            } 

This script adds the new SMTP address for all users within a certain OU.  Of course this will cause some troubles on its own, as there's now going to be two SMTP addresses, marked as primary.

The following script clears this up:

Get-ADUser -SearchBase 'OU=ouname,OU=ouname,OU=ouname,OU=ouname,DC=domai,DC=com,DC=au' -Filter * -Properties mail,ProxyAddresses |
    Foreach {  
        $proxies = $_.ProxyAddresses | 
            ForEach-Object{
                $a = $_ -replace 'SMTP','smtp'
                if($a -match 'newdomain.com.au'){
                    $a -replace 'smtp','SMTP'
                }else{
                    $a
                }
            }
        $_.ProxyAddresse = $proxies
        Set-ADUser -instance $_

    }