Online Fax Security: How Safe Is Sending a Fax Online?
If you are sending sensitive documents -- legal filings, tax forms, medical records, contracts -- you want to know that the method you are using is secure. Fax has a long-standing reputation as a safe way to transmit documents, but does that reputation hold up when you move from a physical fax machine to an online service?
The short answer is yes, but with nuance. Online fax is not inherently more or less secure than traditional fax. The security depends on how the service handles your data at each stage of the transmission. This guide breaks down what actually happens when you send a fax online, where the risks are, and what you can do to protect yourself.
How traditional fax security works
To understand online fax security, it helps to start with how traditional fax works. A conventional fax machine scans your document, converts it into audio signals, and transmits those signals over the public switched telephone network (PSTN) to the recipient's fax machine, which decodes the signals back into an image.
This process is considered relatively secure for a simple reason: intercepting a fax in transit requires physical access to the telephone line, which is significantly harder than intercepting an email. There is no server storing a copy of the document, no inbox that can be hacked, and no password to guess.
That said, traditional fax has its own security gaps. The document prints out on a shared machine where anyone nearby can pick it up. There is no encryption on the telephone line itself -- the signal is transmitted in the clear. And if the fax is sent to the wrong number, the document ends up in a stranger's hands with no way to recall it.
How online fax security works
When you send a fax through an online service like JustFax Online, the process adds an internet segment to the beginning of the transmission. Here is what happens step by step:
1. Upload. You upload your document through a web browser. A well-built service uses HTTPS (TLS encryption) for this connection, which means your file is encrypted in transit between your device and the service's servers. This is the same encryption used by banks and e-commerce sites.
For a step-by-step walkthrough of the full sending process -- from document preparation to delivery confirmation -- see our guide to sending a fax online.
2. Processing. The service receives your document on its servers and converts it into the format required for fax transmission (typically a TIFF image). During this stage, your document exists on the service's infrastructure.
3. Transmission. The service sends the converted document through a fax gateway, which connects to the PSTN and transmits the fax to the recipient's fax machine using the standard fax protocol (T.38 or T.30). This last leg -- gateway to recipient -- travels over the telephone network, just like a traditional fax.
4. Deletion. After successful delivery, a responsible service deletes your document from its servers. JustFax Online deletes files after successful delivery, so your documents are not stored indefinitely.
The key difference between traditional fax and online fax is that middle step: your document temporarily exists on the service's servers. This is where trust in the service matters.
Online fax vs. email: which is more secure?
This is the question most people are really asking. In many cases, fax -- whether traditional or online -- offers practical security advantages over email.
Email is stored in multiple places. When you send an email, copies exist on your mail server, the recipient's mail server, and potentially on backup servers for both. Those copies persist indefinitely unless actively deleted. A fax sent through JustFax Online is deleted after delivery, leaving no permanent copy on the service's servers.
Email is vulnerable to account compromise. If someone gains access to an email account -- through phishing, a weak password, or a data breach -- they can read every message in the inbox, including attachments sent months or years ago. Fax has no equivalent risk because there is no persistent inbox to compromise.
Email often travels unencrypted between servers. While most major email providers now support TLS, encryption between mail servers is opportunistic -- it is not guaranteed. If the recipient's mail server does not support TLS, the message travels in plain text. The upload portion of online fax, by contrast, is always encrypted via HTTPS.
Fax provides delivery confirmation. When a fax is delivered successfully, you receive a transmission confirmation. Email delivery is harder to verify -- a sent message does not mean it was received, read, or not filtered into spam.
That said, email has its own advantages. End-to-end encrypted email services (like ProtonMail or PGP-encrypted messages) can offer stronger security than fax for users who set them up correctly. And email is simply more practical for most everyday communication. The point is not that fax is universally better than email, but that fax remains a legitimate and often preferable option for transmitting sensitive documents -- which is exactly why industries like healthcare, legal, and finance continue to rely on it.
Why regulated industries still use fax
Fax is not just a habit in heavily regulated industries -- it is often a compliance choice. Several regulatory frameworks specifically recognize fax as an acceptable transmission method for sensitive information:
Healthcare (HIPAA). In the United States, HIPAA permits faxing of protected health information (PHI). Many healthcare providers and insurers prefer fax because it avoids the inbox-persistence and account-compromise risks of email.
Legal. Courts, law firms, and government agencies routinely accept faxed filings. Some courts require fax for certain time-sensitive documents. A fax transmission confirmation provides a timestamp that can serve as proof of filing -- see our guide to faxing legal documents for more on this.
Financial services. Banks, brokerages, and insurance companies frequently use fax for document exchange, particularly for forms requiring signatures.
Government. Tax agencies like the IRS accept faxed forms for many filings. Our guide to faxing to the IRS covers which forms can be faxed and the correct numbers to use.
The common thread is that these industries need a transmission method that is point-to-point, provides delivery confirmation, and does not leave persistent copies in vulnerable inboxes. Fax -- including online fax -- fits that requirement.
What to look for in a secure online fax service
Not all online fax services handle security the same way. Here are the things that matter most:
HTTPS encryption for uploads. The connection between your browser and the service should be encrypted with TLS. You can verify this by checking for the padlock icon in your browser's address bar. JustFax Online uses HTTPS for all connections.
File deletion after delivery. Your documents should not live on the service's servers any longer than necessary. JustFax Online deletes files after successful delivery.
No account required. Services that require you to create an account introduce an additional attack surface -- your account credentials and any documents stored in your account. JustFax Online requires no account and no subscription, which means there is no inbox for an attacker to target.
Minimal data retention. A good service retains only what it needs for billing and delivery confirmation, not the content of your faxes.
Reputable payment processing. Payment should be handled through established, PCI-compliant processors. JustFax Online supports major credit cards, PayPal, Apple Pay, Google Pay, and other payment methods, all processed through secure third-party providers.
What you can do to protect yourself
Regardless of the service you use, there are practical steps you can take to improve the security of your faxed documents:
Verify the fax number before sending. The most common security failure in faxing is sending to the wrong number. Always confirm the recipient's fax number from an official source -- their website, letterhead, or direct communication. This is especially important for international faxes, where number formatting mistakes are common.
Use a cover sheet with a confidentiality notice. A cover sheet identifies the intended recipient and can include a confidentiality statement directing anyone who receives the fax in error to contact you and destroy the document. This is standard practice for legal, medical, and financial faxes.
You can send secure faxes from your phone just as easily as from a computer -- the same HTTPS encryption applies. If you need to scan and fax a document on the go, our guide to faxing from your phone covers scanning tips for iOS and Android that help maintain document quality.
Send during business hours. If you are faxing to a shared machine in an office, timing your fax so someone is available to retrieve it reduces the chance of the document sitting unattended. Consider the recipient's time zone, particularly for international faxes.
Alert the recipient. For highly sensitive documents, notify the recipient by phone or email that a fax is coming so they can watch for it.
Keep your confirmation. Save the delivery confirmation as proof of successful transmission. This is especially important for legal filings and tax documents.
Frequently asked questions
Is online fax more secure than traditional fax?
Neither is categorically more secure -- they have different risk profiles. Traditional fax avoids server storage but prints on shared machines and transmits unencrypted over phone lines. Online fax adds HTTPS encryption for the upload and deletes files after delivery (with a responsible service), but temporarily stores the document on servers. For most practical purposes, the security is comparable.
Is fax more secure than email?
For sensitive documents, fax has practical advantages: no persistent inbox to compromise, delivery confirmation, and automatic deletion of the document after delivery (with services like JustFax Online). Email is more convenient for everyday communication, but its persistence and vulnerability to account compromise make it less ideal for sensitive transmissions.
Does JustFax Online store my documents?
No. JustFax Online deletes your files after successful delivery. There is no account, no inbox, and no document archive. The service retains only what is needed for billing and delivery confirmation.
Can someone intercept my online fax?
The upload from your device to the fax service is encrypted via HTTPS. The final leg from the fax gateway to the recipient's machine travels over the telephone network, which is the same as a traditional fax. Intercepting a fax on the telephone network requires physical access to the phone line, which is difficult and uncommon.
Is fax HIPAA-compliant?
Fax is recognized as an acceptable method for transmitting protected health information under HIPAA. However, HIPAA compliance depends on the overall handling of the information, not just the transmission method. Healthcare providers should follow their organization's policies for faxing PHI, including using cover sheets and verifying fax numbers.
Should I use a cover sheet for sensitive faxes?
Yes. A cover sheet identifies the intended recipient and can include a confidentiality notice. This is standard practice for legal, medical, and financial documents and helps protect the information if the fax is delivered to the wrong number or picked up by the wrong person.