A fax server is a set of software running on a server computer which is equipped with one or more fax-capable modems attached to telephone lines or, more recently, software modem emulators which use T.38 (Fax over IP) technology to transmit the signal over an IP network. Its function is to accept documents from users, convert them into faxes, and transmit them, as well as to receive fax calls and either store the incoming documents or pass them on to users. Users may communicate with the server in several ways, through either a local network or the Internet.

Advantages over paper fax machines

• Users can send and receive faxes without leaving their desks.
• Any printable computer file can be faxed, without having to first print the document on paper.
• The number of fax lines in an organization can be reduced, as the server can queue large numbers of faxes and send each when any of a number of lines is free.
• Faxing capability can be added easily to computer programs, allowing automatic generation of faxes.
• Transmitted faxes are more legible and professional-looking.
• There is less clutter of office equipment; incoming faxes can be printed on a standard computer printer.
• Faxing may be monitored and/or recorded, so that users may be allocated quotas or charged fees, or to ensure compliance with data-retention and financial laws.
• Fax Servers can be located centrally in an organization’s data centers providing resilience and disaster recovery facilities to a traditionally desktop technology.
• Incoming junk faxes are not as much of a problem; the server may maintain a blacklist of numbers it will not accept faxes from (or a white list listing all the numbers it will accept calls from), and those that do get through do not waste paper.
• Incoming faxes can be handled electronically as part of a paperless office scheme, reducing or eliminating paper use.