It is forbidden to speak Rechilut, even if the information is true in its entirety. It is also Rechilut regardless of whether the information is spoken in the presence of the subject (i.e. the offending party) or not, even if the speaker would feel comfortable relating the information in front of the subject.
Certainly if one is so brazen to speak Rechilut in front of the subject ("You said ... about him/did ... against him."), it is forbidden, and a more severe transgression. First, he introduces intense hatred into the heart of the listener about the issue, for the listener will accept the information as absolute truth (since he will assume that no one would be so brazen to say what he did right in front of the subject unless it was true). Also, the speaker causes himself and two others (at least) to take part in the speaking of Rechilut, violating many prohibitions explicitly stated in the Torah.
[At the end of this paragraph, the Chafetz Chaim refers to part of the introduction to the book, in which he enumerates the many transgressions that are committed in the scenario above. For example, the speaker violates "do not go about as a talebearer among your people (Lev. 19:16)," and causes the listener to believe the information and thereby violate "do not carry false rumors (Ex. 23:1)," at which point the listener denigrates the subject for what he believes was done against him, violating "do not wrong one
another (Lev. 25:17)." There are actually more prohibitions violated at each point, and as the conflict escalates so do the transgressions; you get the idea. It is important to note that the above method isn't even appropriate for rebuke, due to the public shame it causes the subject (cf. Lev. 19:17 regarding rebuke without causing embarrassment).]
If Reuven said something against Shimon to Levi, and Levi told Shimon what was said [which is a violation of "lo telech rachil b'ameicha" - "do not go about as a talebearer among your people," the principal prohibition against Rechilut], it would be forbidden for Shimon to go back to Reuven and discuss the matter. If Shimon were to approach Reuven, he would also be guilty of speaking Rechilut, in this case because he will make Reuven angry at Levi for repeating what he originally said.
Even if Shimon wouldn't mention Levi's name, but instead said "I heard you said ... about me," it would most likely be obvious to Reuven that the information was repeated by Levi.
Lamentably, we make many mistakes in this area, keeping the Rechilut going around and stirring up more hatred.
[*The abbreviation ch"v, stands for Chas V'Shalom, a phrase meaning "Heaven forfend" in modern Hebrew.]
It's Rechilut even when not said to the victim
Speech can be classified as Rechilut even if it isn't spoken directly to the one involved. If the speaker would relate what one person said about another to a friend of the "victim," it would result in the victim hearing what happened and therefore causing ill will between the victim and the one who originally spoke about him.
Repeating what so-and-so said about one's children or relatives would certainly be forbidden, as it is human nature for the listener to take personal offense to such information and would therefore be classified as Rechilut.
Even if the speaker were to ask his listener(s) to keep the information private, and he were to know that he can trust them not to repeat it, he should refrain from discussing it with them. It may reflect negatively upon the speaker or the listener, and therefore be Lashon Hara.
Propagating "new" Rechilut is prohibited
If one's intention is that the listener should rebuke the person who spoke L"H, refer to Hilchot Lashon Hara 10:5.
In that section we mentioned that one can speak L"H to rectify or prevent other L"H only if the victim already knows what was said about him. If he is unaware that someone is speaking inappropriately about him, and others repeat the information (even for the sole purpose of stopping the talk), it will inevitably get
back to the victim, causing both his embarrassment and his anger toward the person speaking about him. Causing ill will in this way is Rechilut, despite positive intentions.
For further iyun (depth): The commentary Netiv Chayim notes that based on Hilchot L"H 10:5, rebuke is not sufficient purpose to speak Rechilut. He adds that perhaps this is only in the case of passing on information publicly, but telling an individual for the purpose of rebuke would be permissible (provided he will not let the subject of the original L"H find out).
However, the Netiv Chayim continues: "...perhaps a typographical error occurred, and the Chafetz Chaim is referring to chapter 10, paragraph 6..." in which he says it is permitted to warn others that someone is speaking L"H. Then when the individual tries to tell them his story, the listeners will respond with rebuke. The Netiv Chayim says that if the Chafetz Chaim was referring to this case, then Rechilut would be permitted in order to prevent further L"H from being spoken against the victim.
A possible resolution might be that the Chafetz Chaim was referring us to the section, since both paragraphs were relevant. However, since hastily following the advice in paragraph 6 could cause
problems, only paragraph 5 containing the precautions was mentioned to encourage its use as a starting point. -ES