$windowsIdentity = [System.Security.Principal.WindowsIdentity]::GetCurrent()
$windowsPrincipal = new-object 'System.Security.Principal.WindowsPrincipal' $windowsIdentity
if ($windowsPrincipal.IsInRole("Administrators"))
{
# Put your email logic here.
}
Just assign a login script in ADUC, and have it do whatever. A common config is to just append username and time to a text file on the network.