example.ps1

$SourceFile = (Import-Csv -Delimiter ";" -Path).DistinguishedName
#now $sourcefile is already smaller

foreach($User in $SourceFile)
{
    $HomeServer = Get-ADUser -Identity $User -Properties msExchHomeServer, DistinguishedName, userPrincipalName, mail, ObjectClass
    #Try Get-AD-User, Get-ADObject and 
    #ADSI provider (see http://social.technet.microsoft.com/wiki/contents/articles/4231.working-with-active-directory-using-powershell-adsi-adapter.aspx)
    #instead of Get-QADObject. Might perform better, might not. You have to test it. :)
    #Always get only those properties that you'll need later!

    If($HomeServer.msExchHomeServerName -eq 0)
    #I think you don't need "Length" here, do you?
    {
        [PSCustomObject]@{
            DistinguishedName = $HomeServer.DistinguishedName
            userPrincipalName = $HomeServer.userPrincipalName
            mail = $HomeServer.mail
            ObjectClass = $HomeServer.ObjectClass
        }
        #Instead of selecting the required properties and writing it directly out to a CSV file, you are creating a PSObject in this case.
    }
}