One of the greatest gifts Hashem has given the Jewish People is the ability to cleanse ourselves of our sins through teshuvah (repentance). This gift is especially precious when one has been guilty of speaking loshon hora.
We have learned that when we speak loshon hora, we cause untold damage to ourselves, to our listeners and to the subject(s) of our words. The Chofetz Chaim has chronicled in detail the many sins which can be transgressed through loshon hora. Yet regardless of how grievously we have sinned, Hashem extends to us the gift of teshuvah, enabling us to repair the damage, at least to some degree.
The Chofetz Chaim discusses the parameters of teshuvah as it applies to loshon hora. If one has spoken loshon hora but his listeners did not believe what was said, then the sin is one between man and Hashem. Teshuvah in such a case requires that the person regret his sin, confess it before Hashem, and accept upon himself never to repeat it.
If, on the other hand, the loshon hora was accepted as fact and it resulted in harm, then more is required. For example:
A person lost an opportunity for a promotion because someone provided unnecessary or inaccurate, negative information about him. This constitutes real damage, both monetary and emotional. In this case, the three-part teshuvah outlined above would not be sufficient. One would also have to approach the victim and ask forgiveness for having spoken against him and caused him harm.
Certainly, this is a very difficult thing to do, especially if the victim had been unaware that he was being considered for a promotion. Nevertheless, the Chofetz Chaim informs us that neither Yom Kippur, nor death itself, can erase a sin between man and his fellow man unless sincere forgiveness is sought and it is granted.
(The legendary founder of the Mussar Movement, Rav Yisrael Salanter, found difficulty with the above law. From a Mussar perspective, he suggested that if by telling a person that we spoke loshon hora about him, we will cause additional pain and distress, then perhaps it is better not to inform him).
The Chofetz Chaim sees this as one of the major pitfalls of speaking loshon hora. Often, people forget about whom they have spoken, or are unaware of the damage their words have caused. In such cases, warns the Chofetz Chaim, they will never have the opportunity to achieve complete teshuvah.
The Chofetz Chaim further cautions that we should be exceedingly careful not to malign entire families. This kind of loshon hora can create a bad reputation for the family which can last for generations and cause untold hardship.
The Chofetz Chaim once suggested the following for a person who wanted to repent for having spoken loshon hora, but could not remember about whom he had spoken: Such a person should become involved in spreading the teaching of shmiras haloshon. In this way, he will atone, to some degree, for the harm which his own words have caused.