how to let a user write a message and then save it to a file

hi   I'm new to autoit and can you tell me how to let a user write a message and then save it to a file
this is what i've coded so far and its working fine but its not suitable for a longer message with multiple lines
can you tell me how can i do that
thank you

#include <File.au3>
$var = "msg.txt"
$num = InputBox("email address", "please enter your email address", "r2dak@exmaple.com", "",270,130)
$txt= InputBox("write your text ", "Write your Message", "your text here", "",270,130)
_FileWriteToLine($var, 1, "name: " & $num , 1)
;_FileWriteToLine($var, 13, "Date:" & $dnt , 1)
_FileWriteToLine($var, 2, "msg :" & $txt , 1)
MsgBox(64, "Thank you","thanks we will respond soon")