The problem with mailto is that there is a limit to how many caracter you can send... so if you want to format a mail with a long body... it will not work with mailto
But it seems that you are right that there is no way to do this with PHP.
There is a way to open outlook with a formatted mail, but it opens on the server and not on the client 🙁
$objApp = new COM("Outlook.Application");
#Get the application name and version
print "Application name: {$objApp->Application->name}<br />" ;
print "Loaded version: {$objApp->Application->version}<br />";
$myItem = $objApp->CreateItem("0");
$a=$myItem->Recipients->Add("paul.rogers@mowlem.com");
$myItem->Subject="Test the PHP/COM with Outlook";
$myItem->Body="This is a Body Section now.....!";
$myItem->Display();
:glare: