Active Directory Powershell - whole forest script search using .csv user list

I'm looking for a little help, hope no one will bash me for being clueless. Not so long ago I became something of an AD administrator, the organization is large, so the tasks are different. Most of the time I can easily accomplish what I need with Powershell or a snap. However, I have a task on my hands that surpasses my "creativity". I have a list of over 10,000 users in .csv that I need to look for in my local AD if they exist. My two problems: -I am very new to scripting and increasingly frustrated that I cannot figure this out and get my scripts to work the way I need them. -Delivery for this task and other responsibilities give me a little time to learn more about scripting basics and learn.Therefore, in most cases I am forced to search for script fragments on the Internet and modify them a little to suit my needs. This has worked so far as the script I have in my hands is too complex for me.

The biggest problem I've faced so far is finding the forest as a whole. My organization has one root domain and 4 child domains. When running a simple foreach loop like below:

ForEach ($User in (Import-Csv c:\users\public\users.csv))
{ If (Get-ADUser $User.mail -server GLOBALCATALOGADDRESS:xxxx)
{ Write-Host "User found: $($User.mail)"
}
Else
{ Write-Host "User not found: $($User.mail)"
}
}

      

        
        
        
      

    

It only looks for the domain my computer is connected to. So I was able to find and modify a forest-wide search script and came up with the following:

     #Get Domain List
$objForest = [System.DirectoryServices.ActiveDirectory.Forest]::GetCurrentForest()
$DomainList = @($objForest.Domains | Select-Object Name)
$Domains = $DomainList | foreach {$_.Name}
$User = Import-CSV c:\users\public\users.csv
    #Act on each domain
foreach($Domain in ($Domains))
{
Write-Host "Checking $Domain" -fore red
$ADsPath = [ADSI]"LDAP://$Domain"
$objSearcher = New-Object System.DirectoryServices.DirectorySearcher($ADsPath)
    #The filter
Foreach($mail in($User))
{
$objSearcher.Filter = "(&(objectCategory=user)(mail=$User.mail))"
$objSearcher.SearchScope = "Subtree"

$colResults = $objSearcher.FindAll()

foreach ($objResult in $colResults)
    {
    $objArray = $objResult.GetDirectoryEntry()
    write-host $objArray.mail 
    }
}
}

      

        
        
        
      

    

The script seems to be good in its original form (here: http://powershell.nicoh.me/powershell-1/active-directory/forest-wide-object-searches ) and works well with wildcards and one parameter as a filter. However, I have no idea what I am missing so that it searches every email address I have .csv and that it returns information about whether a user with such a mail was found. The script runs itself, but given the time it takes and the empty output, it looks like it is looking for just one user. I'm 100% sure that at least one user on the list exists in on-prem AD. Any suggestions are greatly appreciated. Thanks for your attention.

[EDIT] Final script:

#Get Domain List and load user e-mails from file
$objForest = [System.DirectoryServices.ActiveDirectory.Forest]::GetCurrentForest()
$DomainList = @($objForest.Domains | Select-Object Name)
$Domains = $DomainList | foreach {$_.Name}
$Users = Import-CSV c:\users\public\users.csv
#Act on each domain
foreach($Domain in ($Domains))
{
    Write-Host "Checking $Domain" -fore red
    Foreach($mail in ($Users.mail))
    {
      Get-ADUser -filter {mail -eq $mail} -Server $domain -properties mail | select mail
    }
}