changing mail server/mx records for mail script

hey everyone, hoping to get some help with this.
i'm building an application that sends out newsletters to users for a client and it sends great using mail(). the problem is that the server seems to be sending from a public server or soemthing and the host is being threatened to be labeled at a spam server/dirty ip.

i've been contacted by the host to use the following mx record "mta6.xxx.xxxxx" but have no idea how to set this in the script.

the crappy host is a win/apache/php5 machine and doesn't allow me to log into it to alter things (don't ask me, i've complained to my boss before he still wants the server like this), i would imagine that it's possible to alter this in the php.ini, but i can't access that. so i thought maybe doing something like this:

ini_set("SMTP","smtp.example.com" );
ini_set('sendmail_from', 'user@example.com');


but i'm a little afraid to touch anything at this point because if it still sends emails from the wrong place we could be blocked.

any advice?


phpinfo() seems to understand what i'm trying to do so i'll try with that.