Formatting 'body' using mailto: command

Using the 'mailto:' command I'm trying to format a 'default' message something like... $msg_body = "?subject=whatever&body=This%20is%20the%20default%20part%20of%20the%20message%20..." and soon on but I want to force some 'newlines' into the resultant message body but to no avail. If I just put \n in the message it only reads up until the '\' and nothing after (which is also why I have to use the '%20' for every space in the string). If I put the hex '%5E%6E' it puts the \n literal in the message. Any suggestions? - besides using mail()!