You should Enable mails from MT account center.enable mails? eh? could you be more specific please
In some cases the SMTP servers requires authentication …
There is no way to set on php.ini file the password. You will need to use some PHP script as SMTP php class in order to set your password and access remote SMTP server at mt.
Download and install the php pear mail function which includes an smtp login (I use it for my newsmail thingy) and then search for some sample pear smtp scripts and try it with a simple smtp account. (google it all and everything you need should be near the top)