For material to be defamatory it must be published to a person who is capable of understanding its defamatory significance. A letter is not published if it is in a language unknown to the reader. A letter read only by, and insulting only to, the person to whom it is addressed is not published. Defamatory material is published when it is communicated to someone other than the person it defames.
The publication must be intended to be, or the natural and probable consequence of, the initial actions of the person responsible for the defamation. If a thief steals a defamatory letter from a briefcase and reads it, or if a sealed envelope marked personal and confidential is opened and read by the victim's spouse, there is no publication. On the other hand if a person takes no reasonable precautions to avoid being overheard but instead talks loudly so others can hear the defamatory words this will amount to publication.
As publication involves no more than being responsible for communicating a statement, more than one person can be liable for the publication of defamatory material. An author, a printer and a publisher all publish a libel, and so does a distributor who knows that the material being distributed contains something that is defamatory. Every separate printed copy that is distributed is a separate publication.
The law in this area is developing, particularly in relation to the internet. For example, recent cases suggest that search engines such as Google and Yahoo! could be classified as publishers and be sued for defamation, however it is likely that, in most cases they would have a defence of an innocent disseminator [see Trukulja v Yahoo! Inc LLC & Anor  VSC 88].