C++ is a compiled language. Either you hard code it, pass it in from the command line, read it from a file, or prompt the user for it. Those are about your only choices.
2) You're attempting to copy something into a const char *.
It doesn't look like you're thinking clearly about what your variables are for. What is the message parameter supposed to be for? What is MAIL_MESSAGE supposed to be for? What is MAIN_EMAIL_MSG supposed to be for?
Also, please use code tags when posting code, to make it readable: