By David Thompson · Published December 2, 2025 · Updated June 8, 2026 · 5 min read
A fax machine scans a document, converts the image into audio-frequency tones, and transmits those tones over a telephone line to a receiving machine that prints a paper copy on the other end. That is the core of what a fax machine does — and it has worked this way since the technology became mainstream in the 1980s.
Despite the rise of email and cloud storage, fax machines remain in active use across healthcare, law, and government. Understanding what they do — and how they do it — helps you decide when to use one and when a modern alternative makes more sense.
What a Fax Machine Does (in Plain English)
A fax machine is a device that sends and receives copies of documents over a standard telephone line. It works like a combination of a scanner, a modem, and a printer wrapped into one unit.
When you place a document in the fax machine and dial a number, the machine:
- Scans the page and reads it as a grid of black and white dots
- Converts those dots into audio tones that travel over the phone line
- Sends the tones to the receiving fax machine
- Receives a confirmation that the document arrived
The machine on the other end does the reverse — it decodes the tones and prints the document. The result looks nearly identical to the original, though early fax machines produced lower-resolution output than modern ones.
A Quick History Note
The first fax machine patent was filed by Scottish inventor Alexander Bain in 1843 — before the telephone even existed. Modern commercial fax machines took off in the 1980s, with peak usage in the 1990s before online alternatives emerged.
How a Fax Machine Works Step by Step
Understanding the full mechanics of how a fax machine works is easier when you break it into four phases.
1. Scanning the Document
When you load a page into the fax machine, a sensor inside scans the document one thin horizontal line at a time. Each pixel in that line is read as either black or white — fax machines do not transmit color. The result is a bitmap representation of your document.
2. The Handshake
Before any document data is transmitted, the two fax machines must establish a connection. The sending machine dials the receiving machine's fax number and both machines exchange a series of tones — you may recognize this as the distinctive screeching sound fax machines make. This "handshake" confirms that both devices can communicate and agrees on transmission speed and format. It takes roughly 3–5 seconds.
3. Transmitting the Signal
Once connected, the sending machine's modem converts the scanned image data into audio-frequency tones and sends them over the phone line at speeds between 9,600 and 33,600 bits per second. A standard single-page document takes 30 seconds to a few minutes to transmit, depending on image complexity and line quality.
4. Receiving and Printing
The receiving fax machine's modem demodulates the incoming tones back into binary image data. The built-in printer then reproduces the document — most commonly on thermal paper (heat-sensitive paper that darkens without ink) or plain paper via an inkjet or laser mechanism.
After printing, the receiving machine sends a confirmation signal back to the sender. This creates a verifiable delivery record, which is one of fax's key legal advantages over email.
What Are the Main Parts of a Fax Machine?
A standard fax machine contains four core components:
| Component | What It Does |
|---|---|
| Scanner | Reads the document as a black-and-white pixel grid |
| Modem | Converts image data to audio tones for transmission (and back) |
| Printer | Prints received documents — thermal or plain paper |
| Control panel | Lets you dial numbers, set options, and review the send log |
Some models also include a telephone handset so the machine doubles as a phone, and a memory buffer that stores documents when the line is busy.
What Is a Fax Machine Used For?
Fax machines are used to send official documents that require a verifiable paper trail. Common use cases include:
- Healthcare: Sending patient records, referrals, and prescriptions between providers. Approximately 70% of healthcare communication still flows through fax due to HIPAA compatibility and EHR system integration.
- Legal: Filing contracts, court documents, and signed agreements
- Government: Submitting forms to the IRS, Social Security Administration, and other agencies that still accept or require fax
- Real estate: Transmitting purchase agreements and disclosure documents with signatures
- Finance: Processing loan documents and insurance claims
Why Fax Persists in These Industries
Fax transmissions travel over dedicated phone lines, making them inherently more difficult to intercept than email. They also produce a timestamped delivery receipt — a legal record that the document arrived. Email cannot replicate this by default.
If you need to learn how to use a fax machine for the first time, the process is straightforward: load the document, dial the number, and press Send.
Fax Machine vs. Online Fax: What Is the Difference?
A traditional fax machine requires a phone line, a power outlet, thermal paper, and a fixed location. You can only send and receive faxes when you are physically present at the machine.
Online fax services — like mFax — deliver the same result without any hardware. They convert your document into a fax signal digitally and route it through the same telephone infrastructure. You send from your phone, laptop, or browser. The recipient receives a standard fax, indistinguishable from one sent by a physical machine.
| Feature | Physical Fax Machine | Online Fax (mFax) |
|---|---|---|
| Hardware required | Yes (machine + phone line) | None |
| Send from mobile | No | Yes |
| Cost to get started | $100–$500+ for machine | Free trial |
| Maintenance | Paper, ink, phone bill | None |
| Delivery confirmation | Printed report | Digital receipt |
| HIPAA compliant option | Requires extra setup | Built in (mFax Business) |
For a detailed breakdown of running costs, see our fax machine cost guide. If you are comparing services instead, our best online fax services comparison covers the top options side by side.
Skip the Hardware
mFax lets you send and receive faxes from your phone in under 2 minutes — no machine, no phone line, no paper. Over 5 million users have switched.
Is Faxing Still Relevant?
Yes — more than most people expect. According to a 2024 Statista report, approximately 17% of businesses globally still rely on faxing for critical operations. In healthcare, that figure rises to 70%. The online fax market is projected to grow from $2.88 billion in 2026 to $5.18 billion by 2035.
The fax machine as a physical device is declining, but faxing as a transmission standard is not. Online fax services have modernized the technology — keeping the legal and compliance benefits while removing the hardware. Read more in our is faxing still relevant guide.
Send Your First Fax Now
You do not need a fax machine to send a fax. Download the mFax app, upload your document or snap a photo, enter the fax number, and send. Delivery confirmation arrives within minutes.
For businesses needing HIPAA compliance, team accounts, and virtual fax numbers, mFax Business starts at about $9/mo (billed annually) — fully customizable, so you build your own plan by choosing the exact seats and pages you need and paying only for what you use, with no fixed tiers.