jakob.ps1

$users = Get-ADGroupMember G_Email_Archive_2013 | Select-Object -ExpandProperty name
foreach ($user in $users) 
{
    # Extract Mailbox GUID and pipe to variable $GUID 
    $GUID = Get-Mailbox $user | select ExchangeGUID 
    $customAttrib3 = Get-Mailbox -Identity $user -CustomAttribute3 -ErrorAction SilentlyContinue
    if($customAttrib3)
    {
        #dersom CustomAttrib3 har verdi, så kan vi gjøre noe her
    }
    else
    {
        #customattrib3 er tom, sett verdi
        set-mailbox $user -CustomAttribute3 "iXOS-EXLK:/{$($GUID.ExchangeGuid)}"
    }
}