The issue is with your recordsets on lines 48-76. You are using IN statements for your queries and my best guess is that they aren't returning values. I'm not sure why you are using an IN statement since it is only sending a single value to the query.
My guess is that one of the earlier recordsets aren't returning a value which is resulting in an empty IN statement and that is the cause of the error. I'm sure it has nothing to do with the email unless you have another recordset in the email body file that I haven't seen.
If you give me FTP access and a full URL to reproduce I could debug it more. (I'd write the SQL statements to the page before each mysql_query() line like:
$query_smsBookingDetails = "SELECT BookingID, PickUpID, DriverID FROM Bookings WHERE BookingID IN (".$_GET['BID'].")";
$smsBookingDetails = mysql_query($query_smsBookingDetails, $con1) or die(mysql_error());
and so on for the others.
That will write the SQL statements before the error and allow you to diagnose at least which is causing the problem.