Warrantless mail searches may be allowed??

I was a Customs Officer

Ohh nice.. So you definitely know bout it then...that's cool

so if America obtains information that 'may' be of benefit to it in some form, will they legally have to declare the source of the information coming from intercepted mail?

For the purposes of intelligence gathering? Absolutely not. No one but the CIA/FBI/NSA/etc even knows what information they have.

They *will* have to disclose the source of the information if they wish to use it in a trial or prosecution of some sort.. and it's more than possible that such evidence would be thrown out of court because it was obtained illegally (ie, without a warrant).

Of course, certain new rules allow people to be detained indefinitely as "enemy combatants" or "terrorists" or whatever with no trial, no lawyers, etc, but I expect that to change in 2009.