'f:' => 'match within the From header',
'a:' => 'match within the To, Cc, and From headers',
'tc:' => 'match within the To and Cc headers',
'f:' => 'match within the From header',
'a:' => 'match within the To, Cc, and From headers',
'tc:' => 'match within the To and Cc headers',