Well, the first thing I would say is that "porn offers" are pretty easy to come by. Many of those companies collect email addresses and send to whoever they like. (I assume you're talking about email, not regular mail.) So just because your brother gets offers doesn't mean he's interested.

I suggest you find out more about what's going on with your brother by asking him directly. Nobody knows better than he does!

I can see not wanting to "confront" him, but what about something more casual? Maybe bring it up when you're alone and both kind of relaxed. You could ask him if he gets pornography and if he says yes, ask him about it.

Your brother may very well be interested in pornography. And that's something you should probably take into account when you're thinking ahead about having this conversation. How will you feel if says he does like porn? How will you feel if he says it's none of your business?

Of course, whatever your brother tells you and whatever you decide to tell him about how you feel, there's not a lot you can do about the porn itself. Unless he's very young, he has a right to his privacy. (Which also means you probably shouldn't be going through his mail!)