What can users set under the fax sub-tab in printing preferences?

The ability to set third-party fax company links under the fax sub-tab in printing preferences allows users to integrate external services that facilitate faxing directly from within NetSuite. This functionality is particularly useful for organizations that rely on fax communications as part of their business processes. By linking third-party fax services, users can streamline operations, reduce the need for physical fax machines, and enhance the efficiency of document delivery.

The other options do not align with the purposes of the fax sub-tab in printing preferences. Default email templates are related to email communication settings, while font sizes pertain to the visual presentation of printed documents. Rules for invoice generation deal with the automation and criteria of invoice creation, which is separate from faxing capabilities. Thus, the correct answer highlights the integration of external fax solutions within the NetSuite printing preferences.