Query 0n Port 25

Hi Guys,

This is very basic query but have to ask this. Is it necessary to open port 25 for public in exchange env.?Wouldn't it is like opening a gate for whole world to enter into you env. and do the damages to your exchange env. My understanding is that port 25 should be opened only for knows IPs which you trust, not for "Anyone".

Any thoughts on this?

Thanks,

Pinto