So the background problem is that new email is being stored as received on '1970-01-01', right? Try changing file 'environment/classes/mail/MailUtilities.class.php' line 206 from:
if (array_key_exists("Date", $parsedMail)) {
$mail->setSentDate(new DateTimeValue(strtotime($parsedMail["Date"])));
}else{
$mail->setSentDate(new DateTimeValue(DateTimeValueLib::now()));
}
if (array_key_exists("Received", $parsedMail) && $parsedMail["Received"]) {
$mail->setReceivedDate(new DateTimeValue(strtotime($parsedMail["Received"])));
}else{
$mail->setReceivedDate(new DateTimeValue(DateTimeValueLib::now()));
}
to:
$sent_timestamp = false;
if (array_key_exists("Date", $parsedMail)) {
$sent_timestamp = strtotime($parsedMail["Date"]);
}
if ($sent_timestamp === false || $sent_timestamp === -1 || $sent_timestamp === 0) {
$mail->setSentDate(DateTimeValueLib::now());
} else {
$mail->setSentDate(new DateTimeValue($sent_timestamp));
}
$received_timestamp = false;
if (array_key_exists("Received", $parsedMail) && $parsedMail["Received"]) {
$received_timestamp = strtotime($parsedMail["Received"]);
}
if ($received_timestamp === false || $received_timestamp === -1 || $received_timestamp === 0) {
$mail->setReceivedDate($mail->getSentDate());
} else {
$mail->setReceivedDate(new DateTimeValue($received_timestamp));
}