I finally got it to work using %0a@0d. In fact it gave me a double line feed. Why %0a and %0d did nothing mystifies me.
Have you tried %0d%0a, in that order. An end of line is specifically \r\n (0x0d0a) and not \n\r (0x0a0d).
Any version of EndOfLine, whether plain, .UNIX or .windows caused the PHP program to fail and not send the email at all.
PHP is embedded (transported) within HTML, so whatever you send to the PHP processor must conform to the HTML protocol. Whitespace characters have little meaning within HTML.
EndOfLine.Windows equates to a string of the two bytes 0x0d, 0x0A, Which are whitespace ASCII characters, ignored by the HTML parser. Sending the string "%0a%0d", takes 6 bytes but it informs the HTML parser that it needs to substitute the binary bytes (0x0a0d). Similarly "%22" will substitute double quotes, "%09" will substitute a tab character, etc etc.
Sorry if I did not make it clear that you would need to send the line ending sequence as in a way the PHP processor can recognise.