How Does Online Faxing Work?
A Complete Guide
Online faxing lets you send documents to any fax machine in the world without owning a fax machine yourself. You upload a document to a website, the service converts it to the standard fax format, and transmits it over phone lines — just like a physical fax machine would. The recipient gets a printed fax as if it came from a traditional machine.
Up to 45 Pages. $2.75 Flat. No Subscription.
What Is Online Faxing?
Online faxing — sometimes called web-to-fax or internet faxing — is the process of sending faxes through the internet rather than through a physical fax machine. Instead of feeding a paper document into a fax machine connected to a phone line, you upload a digital document (like a PDF) to a website. The online fax service then handles everything that a physical fax machine would: converting your document to the standard fax format and transmitting it over phone lines to the recipient's fax machine.
From the recipient's perspective, there is no difference. Their fax machine rings, connects, and prints your document exactly as if you had sent it from a physical fax machine in your office. The only difference is on your end — instead of a bulky machine, you used a website on your phone or computer.
Online faxing eliminates the need for dedicated hardware, phone lines, toner, paper, and maintenance. It is the same underlying technology, just with a more convenient starting point.
How Does the Technology Work?
Understanding how online faxing works requires knowing what happens at each stage of the process. Here is the technical breakdown:
Document Upload and Conversion
When you upload a PDF to an online fax service, the system converts your document into TIFF (Tagged Image File Format) — the standard image format used by fax machines worldwide. This conversion preserves the visual layout of your document while making it compatible with fax transmission protocols. Every fax machine in the world reads TIFF, which is why this format has been the standard since the 1980s.
T.38 Protocol Transmission
The converted document is transmitted using the T.38 protocol — the international standard for sending faxes over IP networks. T.38 handles the handshake between the sending system and the receiving fax machine, negotiates transmission speed, manages error correction, and ensures the document arrives intact. This is the same protocol used by modern fax machines that connect through VoIP systems.
PSTN Connection
The online fax service connects to the Public Switched Telephone Network (PSTN) — the global network of phone lines — to reach the recipient's fax machine. The service dials the fax number, establishes a connection with the receiving machine, and transmits the TIFF image data page by page. The PSTN is the same network that physical fax machines use, which is why online faxes are fully compatible with any traditional fax machine.
Delivery Confirmation and Retries
After transmission completes, the receiving fax machine sends an acknowledgment signal back through the phone line. The online fax service captures this confirmation and notifies you via email that your fax was delivered successfully. If the recipient's line is busy or does not answer, the service automatically retries — FaxItOnce retries up to 4 times at no additional charge.
How Do I Send a Fax Online?
While the technology behind online faxing is sophisticated, the process for you as a user is simple. With FaxItOnce, sending a fax takes three steps and under 2 minutes:
Upload Your PDF
Select and upload your PDF document. FaxItOnce accepts files up to 45 pages. Upload from your device, cloud storage, or email attachments.
30 sec
Enter the Fax Number
Type in the recipient's fax number. FaxItOnce supports domestic US numbers and select international destinations.
15 sec
Pay $2.75 and Send
Complete a one-time payment of $2.75 through secure Stripe checkout. Your fax begins transmitting immediately after payment.
30 sec
What Happens After I Send?
After you click send and payment is confirmed, your document enters the FaxItOnce transmission queue. Here is what happens next:
Immediate Processing
Your PDF is converted to fax format and transmission begins within seconds of payment confirmation.
Active Transmission
FaxItOnce dials the recipient fax number, establishes a connection, and transmits your document page by page.
Delivery Confirmation
You receive an email notification the moment your fax is successfully delivered to the recipient machine.
Automatic Retries
If the recipient line is busy or unavailable, FaxItOnce automatically retries up to 4 times at no additional charge.
Is Online Faxing as Reliable as a Fax Machine?
Yes. Online fax services use the same underlying technology as physical fax machines — the T.38 protocol and PSTN transmission. The document that arrives at the recipient's fax machine is identical whether it was sent from a physical fax machine or from an online service.
In fact, online fax services often have a reliability advantage over physical machines. A physical fax machine cannot automatically retry if the line is busy — someone has to walk back to the machine and press send again. Online services like FaxItOnce retry automatically up to 4 times, increasing the likelihood of successful delivery without any effort on your part.
Physical fax machines are also subject to paper jams, toner issues, and phone line problems. Online faxing eliminates all of these mechanical failure points.
What File Formats Can I Fax Online?
FaxItOnce accepts PDF files for faxing. PDF is the most widely used document format and preserves your formatting, fonts, images, and layout exactly as intended. If your document is in another format (like a Word document or image), you can convert it to PDF before uploading — most operating systems and applications include built-in PDF export or "Print to PDF" functionality.
How Long Does It Take to Send a Fax Online?
Upload and Payment
Under 2 minutes
Upload your PDF, enter the fax number, and complete payment.
Transmission
1-5 minutes
Fax transmission time depends on the number of pages in your document.
Total End-to-End
Under 10 minutes
From opening the website to confirmed delivery, the typical total is under 10 minutes.
Online Faxing vs. Traditional Fax Machines
Here is how online faxing compares to using a traditional fax machine:
| Feature | Traditional Fax Machine | FaxItOnce (Online) |
|---|---|---|
| Equipment needed | Fax machine ($50-500) | Any device with a browser |
| Phone line required | Yes ($20-40/month) | No |
| Toner and paper | Ongoing expense | Not needed |
| Cost per fax | Phone line + supplies | $2.75 flat |
| Automatic retries | Manual | Up to 4 automatic retries |
| Send from anywhere | Only where machine is located | Any device, any location |
| Maintenance | Paper jams, toner replacement | None |
“Online faxing works by converting your document to the standard fax format (TIFF) and transmitting it over phone lines using the T.38 protocol — the same technology used by physical fax machines. The difference is you do not need a machine, a phone line, or a subscription. With FaxItOnce, the process takes under 2 minutes and costs $2.75.”
Frequently Asked Questions
What is online faxing?
Online faxing is the process of sending faxes via the internet instead of a physical fax machine. You upload a document on a website, and the service converts it and transmits it over phone lines to the recipient fax machine.
How does online fax technology work?
Online fax services convert your uploaded document (such as a PDF) into the standard fax format (TIFF), then transmit it using the T.38 protocol over the public switched telephone network (PSTN) to the recipient fax machine.
Is online faxing as reliable as a physical fax machine?
Yes. Online fax services use the same PSTN transmission and T.38 protocol as physical fax machines. Online services often add automatic retry capabilities — FaxItOnce retries up to 4 times if the recipient line is busy.
How long does it take to send a fax online?
The entire process — uploading your document, entering the fax number, and paying — takes under 2 minutes. Fax transmission itself takes 1-5 minutes depending on page count. Most faxes are fully delivered within 10 minutes end-to-end.
What file formats can I fax online?
FaxItOnce accepts PDF files for faxing. PDF is the most common document format and preserves formatting, fonts, and layout exactly as intended.
Do I need a subscription to fax online?
No. FaxItOnce charges a flat $2.75 per fax with no subscription, no monthly fees, and no per-page charges. Whether you send 1 page or 45 pages, the cost is the same.
Ready to Send a Fax Online?
No fax machine. No phone line. No subscription. Upload your PDF, pay $2.75, and send in under 2 minutes.
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Last updated: February 2026