3. If we just talked about a colleague in the company office, will such a conversation be regarded as publication under defamation law?
Even if the employees of a company are communicating defamatory matters with each other (without further publication outside the company), and even if the contents of the conversation relate to the company's affairs, it can still be regarded as publishing defamatory matter.
However, if the aforesaid communication is made in good faith between a person who has a duty to inform the others of matters that defame the colleague, and the defamatory matter is related to the affairs of the company, a defence known as "qualified privilege" is available to the publisher.
Example: You heard that your colleague (Mr. A) is going to disclose some confidential information about your company to a competitor. You subsequently reported that incident to your boss telling him to take pre-cautionary steps. Although this can be considered defamatory of Mr. A, you have acted in good faith and therefore the defence of qualified privilege may help you avoid liability for defamation.