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Internet fax, e-fax, or online fax is a general term which refers to the use of the Internet to send a document fax, rather than using only phone networks (traditional faxing) with a fax machine. The term "Internet fax" encompasses "web fax" and "email fax," along with VoIP fax, which refers to the use of Voice over Internet Protocol to send a fax. However, Internet fax should not be confused with IP fax.
- no hardware; no software
- no extra telephone line required for fax
- paperless communication, integrated with email
- the ability to store encrypted faxes online securely
- the ability to send and receive multiple faxes simultaneously
- a reduction in phone costs, along with lower costs than traditional fax
- the ability to send and receive faxes from any location that has Internet access
- the ability to send and receive faxes from mobile phones, smartphones and tablets
Note that depending on which method is used, suitable equipment and/or the use of a gateway is required (see below).
Fax has no technical advantage over sending information over the Internet, using technologies such as email, scanner, and graphics file formats; however, it is extremely simple to use: put the documents to be faxed in a hopper, dial a phone number, and press a button. Fax continues to be used over the telephone network at locations without computer and Internet facilities; and sometimes a fax of a document with a person's handwritten signature is a requirement for legal reasons. Computer fax over the Internet allows fax communication without an actual fax machine at either or both ends.
Traditional fax 
- Fax machine → Phone line → Fax machine
A fax machine is an electronic instrument composed of a scanner, a modem, and a printer. It transmits data in the form of pulses via a telephone line to a recipient, usually another fax machine, which then transforms these pulses into images, and prints them on paper.
The traditional method requires a phone line, and only one fax can be sent or received at a time. The phone connection must not be a packet-based system in which delays can occur—a VoIP connection will not work well without special precautions (T.38-compliant equipment at both ends).
Internet fax 
Internet fax achieves a dramatic reduction in communication costs especially when long faxes are frequently exchanged with overseas or distant offices.
Since there is no telephone connection charge when sending a fax over the Internet, the cost of sending faxes is covered entirely by the fixed line Internet connection fee. The recipient machine must also be compatible with Internet fax.
Hardcopy is converted to TIFF or PDF data and attached to an e-mail in MIME format. Then, taking advantage of a connection to the office LAN, data is sent via TCP/IP directly to any Internet Fax on the intranet or Internet. Because they make use of TCP/IP, Internet Faxes do not incur long-distance transmission costs and reception is verifiable.
IP fax and IP address relay 
IP fax is frequently confused with Internet fax, though IP fax transmits data over an office intranet from a networked multifunctional device to the IP address of another. Taking advantage of an established LAN/WAN infrastructure, IP fax reduces or eliminates costly connection and transmission fees. T.38 is a commonly used and recommended transmission standard used for IP fax.
Also, IP fax does not require a dedicated server or make use of the office mail server. IP Address Relay forwards to a multifunctional device for relaying to a local G3 fax machine.
Computer-based faxing 
As modems came into wider use with personal computers, the computer was used to send faxes directly. Instead of first printing a hard copy to be then sent via fax machine, a document could now be printed directly to the software fax, then sent via the computer's modem. Receiving faxes was accomplished similarly.
- Computer → Phone line → Fax machine
- Fax Machine → Phone line → Computer
A disadvantage of receiving faxes through the computer is that the computer has to be turned on and running the fax software to receive any faxes. It also means that the document is no longer readable by computer applications, unless optical character recognition methods are used to read the fax image.
Note: This method is distinct from Internet faxing as the information is sent directly over the telephone network, not over the Internet. This helps to communicate from remote places to the fax machine's location.
Internet fax servers/gateways 
The Internet has enabled the development of several other methods of sending and receiving a fax. The more common method is an extension of computer-based faxing, and involves using a fax server/gateway to the Internet to convert documents between faxes and emails. The process is often referred to as "fax to mail" or "mail to fax". This technology offers the advantage of dispensing with the machine as well as the additional telephone line, and because of this, has started to replace the traditional fax machine.
- Fax machine → Phone line → Fax gateway → email message (over Internet) → computer email account
A fax is sent via the Public Switched Telephone Network (PSTN) to the fax server, which receives the fax and converts it into PDF or TIFF format, according to the instructions of the user. The processed file is then transmitted to the Web server, which sends it as an email containing the fax as an attached file, and sometimes sends a message reporting delivery to a mobile phone.
- Computer → Internet → Fax gateway → Phone line → Fax machine
The user connects to the supplier Web site, specifies the receiving fax number, and uploads the document to send. The document is usually converted to PDF or TIFF format and sent by the Web server to the fax server, which then transmits it to the receiving fax machine via the telephone network. The sender usually receives confirmation that transmission was successful, either in the web interface or by email.
An Internet fax service allows faxes to be sent from a computer via an Internet connection, thanks to a Web interface usually available on the supplier's Web site. This technology has many advantages:
- No fax machine → no maintenance, no paper, toner expenditure, possible repairs, etc.
- Mobility → All actions are done on the Web interface; the service is thus available from any computer connected to Internet, everywhere in the world.
- Confidentiality → The faxes are sent to the recipient's email account, which may be more private than a fax machine used by several people.
- No installation of software or hardware required → the Web interface is used.
- No need for a telephone line for fax use.
- Several faxes can be sent or received simultaneously, and faxes can be received while the computer is switched off.
Fax using Voice over IP 
Making phone calls over the Internet (Voice over Internet Protocol, or VoIP) has become increasingly popular. Compressing fax signals is different from compressing voice signals, so a new standard (T.38) has been created for this. Using a (sending) VoIP adapter and (receiving) gateway which are both T.38 compliant, most fax machines can be plugged into the VoIP adapter in the same way as to a regular phone line. Not all fax equipment claiming T.38 compliance works reliably; in particular communicating with older fax machines (before VoIP began to be used) is problematic.
- Fax machine → VoIP adapter → VoIP gateway → Phone line → Fax machine (or vice versa)
As with regular faxes, only one fax can be sent or received at a time.
Fax using email 
While the needs of computer-to-fax communications are well covered, the simplicity of quickly faxing a handwritten document combined with the advantages of email are not.
- iFax machine → email message (over Internet) → computer email account
- iFax machine → email message (over Internet) → iFax machine (using email address)
A new fax machine (supporting iFax/T.37) is required, as well as a known email address for the sending and receiving machines. This has limited the standard's use, though a system for looking up a fax's email address based on its phone number is under development .
To work with existing fax machines, all iFax machines support standard faxing (requiring a regular phone line). Alternatively, an iFax can be used in conjunction with a fax gateway.
- iFax machine → email message (over Internet) → Fax gateway → Phone line → traditional Fax machine (or vice versa)
See also 
- "Features and Advantages of Sending Faxes by Email". Online Fax to Email. Retrieved 25 August 2012.
- Davila, Damian (4 January 2011). "4 Benefits of Internet Fax". idaconcpts. Retrieved 25 August 2012.
- "Online Fax Service Overview". ChooseWhat. Retrieved 25 April 2013.
- "Online Fax Guide & Internet Fax Reviews". FaxAuthority. Retrieved 25 August 2012.
- softswitch.org: Faxing over IP networks