$Abuse :
Abuses - mails sent to user without their consent
$UnknownUsers :
Users, that could not be reached.
$Opened :
Number of opened messages
$Clicked :
Number of clicked messages
$AverageSpamScore :
Penalty from messages marked as spam.
$ServerFilter :
Content analysis.
$TrackingDomain :
Tracking domain.
$SenderDomain :
Sending domain.