Rabba son of Rav Huna said: Any matter that was said in the presence of three people does not have the status of malicious speech. Why? Your friend has a friend, and your friend’s friend has a friend (i.e. each person will tell someone else).
Many explanations have been offered for this teaching. Rashi appears to indicate that the main concern with regard to evil tidings is when it is done secretly and anonymously. In a situation where it is clear that the statement was made knowing that the identity of the person who said it would be publicized, then it would not fall into the category of forbidden speech. Tosafot argue that it is certainly forbidden to speak badly of another no matter how many people are present. Rabba’s teaching should be understood to mean that if an ambiguous statement is made before three people it is clear that it should be understood as a positive statement and not a negative one. According to Rabbeinu Yona this refers to a case when it is permitted to speak, for example where evil was done to him and he is raising a public objection.
Another law regarding the laws of slander was taught by Rav Dimi upon his return from the Land of Israel. The Gemara quotes him as teaching:
What is the meaning of the verse (Mishle 27:14): “He that blesses his friend with a loud voice, rising early in the morning, it shall be counted a curse to him.” It refers, for example, to the case of one who is invited to a host and they look after him very well, and the next day he goes out into the marketplace and says: “May the Merciful One bless So-and-so, who labored so much on my behalf.” Whereupon people will hear it and come and plunder him.
Rashi explains that we are concerned that the host will be “plundered” by other guests who will want to take advantage of his generous hospitality. Rabbeinu Gershom suggests that once it becomes public knowledge that he is wealthy, the government (or, perhaps, individuals) may try to rob him.